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INFLUENZA 

An  Epidemiologic  Study 


BY 
WARREN  T.  VAUGHAN,  M.D. 


BALTIMORE.   MD. 

THE  AMERICAN  JOURNAL  OF  HYGIENE 

Monographic  Series  No.    1 

1921 


COPYKIGHT,    1921,   BY 

The  American  Journal  of  Hygiene 
bM-timgre,  Md. 


Press  of 

The  New  Eba  Printing  Company, 

Lancaster,  Pa. 


PREFACE. 

Following  every  widespread  epidemic  or  pandemic  of  influenza, 
the  contemporary  literature  becomes  virtually  flooded  with  reports  of 
scientific  studies  on  the  etiology  and  the  epidemiology  of  the  disease. 
By  the  time  that  recrudescences  have  ceased,  interest  has  usually 
lagged  and  eventually  research  in  this  subject  has  practically  ceased, 
only  to  be  revived  with  the  development  of  the  next  extensive  epidemic. 

To  one  who  has  had  occasion  to  review  the  extensive  literature  of 
the  last  pandemic,  it  becomes  apparent  that  many  of  the  recent  writers 
are  uninformed,  or  at  best  only  partially  informed,  regarding  the  rather 
extensive  information  accumulated  during  the  1889  epidemic.  The 
longer  one  studies  the  observations  made  in  1889-93  the  more  firmly 
convinced  one  becomes  that  the  recent  piandemic  was  identical  with 
the  former  in  practically  all  of  its  manifestations. 

It  is  desirable  that,  following  each  epidemic  prevalence  some  indi- 
vidual or  individuals  review  the  literature  of  the  preceding  epidemics, 
acquaint  himself  with  what  has  been  written  regarding  influenza  in 
the  intervening  time  up  to  the  epidemic  prevalence  and  correlate  the 
work  done  in  these  two  periods  with  the  various  reports  regarding  the 
latest  epidemic. 

The  following  pages  constitute  an  attempt  to  correlate  the  epide- 
miologic observations  of  the  epidemic  thirty  years  ago  with  those  of 
the  1918-20  epidemic,  and  with  the  observations  made  during  the 
intervening  years. 

The  house  census  in  the  City  of  Boston  and  the  preparation  of 
this  monograph  were  made  possible  by  the  financial  assistance  of  the 
Metropolitan  Life  Insurance  Company.  This  organization  has  de- 
voted a  considerable  sum  of  money  to  the  study  of  influenza  in  its 
various  phases. 

The  author  is  indebted  to  his  chief.  Dr.  Milton  J.  Rosenau,  for 
helpful  advice  and  criticism  and  for  the  inspiration  to  carry  on  this 
investigation.  Dr.  W.  H.  Frost  has  made  many  valuable  suggestions. 
Appreciation  is  also  due  Mr.  Edwin  M.  Knights,  who  is  responsible 
for  all  of  the  charts,  and  to  Mrs.  V.  K.  Davis,  w^ho  aided  in  the  tabula- 
tion of  results  of  the  Boston  investigation. 


iv  PREFACE 

The  house-to-house  census  was  carried  out  with  the  co-operation 
and  assistance  of  the  Federated  Jewish  Charities  in  Boston  and  indi- 
vidual members  of  the  spcial  service  departments  of  the  Massachusetts 
General  Hospital  and  the  Peter  Bent  Brigham  Hospital. 

The  Author. 

Department  of  Preventive  Medicine  and  Hygiene, 

Harvard  Medical  School,  Boston, 

September  17,  1920. 


^HIS  monograph  is  one  of  a  series  of  studies  carried  out  under  the  super- 
vision of  the  Influenza  Commission  of  the  Metropolitan  Life  Insurance 
Company.  The  Influenza  Commission  is  investigating  the  etiology  and  pre- 
vention of  the  acute  respiratory  diseases,  and  the  work  is  being  carried  on 
in  Boston,  New  York  City,  Chicago,  and  Washington.  The  members  of  the 
Commission  are  Dr.  M.  J.  Rosenau,  Chairman,  Dr.  G.  W.  McCoy,  Dr.  L.  K. 
Frankel,  Dr.  A.  S.  Knight,  Dr.  E.  0.  Jordan,.  Dr.  W.  H.  Frost  and  Dr.  W. 
H.  Park,  Secretary, 


INFLUENZA. 
AN  EPIDEMIOLOGIC  STUDY.* 

By  WARREX  T.  VAUGHAN,  M.  D. 
(Received  for  publication  April  6th,  1921.) 

(ONTENTS 

SECTION  I. 

Page 

General  Epidemiologic  Considerations 1 

Historical 2 

Clinical  and  epidemiologic  identification 13 

General  characteristics  of  early  epidemic  outbreaks 14 

Symptoms  in  former  epidemics 19 

Manner  of  spread 20 

Human  intercourse 23 

Crowd  gatherings 26 

Mass  attack 27 

Healthy  carriers  and  convalescents 30 

General  manner  of  spread  in  individual  localities 31 

Primary  type  of  epidemic 31 

Secondary  type  of  epidemic 33 

Mortality  curves 36 

Duration  of  explosive  outbreak ; 37 

Morbidity  curves  in  1920  recurrences 41 

Spread  in  countries  and  continents -42 

Spread  in  primary  waves 42 

Spread  in  recurrences 44 

SECTION  II. 

Influenza  Epidemics  Since  1893 47 

Occurrence  since  1893 47 

Period  from  1893-1918 47 

Increase  in  1900-1901 49 

Period  from  1901-1915 51 

Influenza  in  1915-1916 55 

Influenza  between  1916  and  1918 58 

*  From  the  Department  of  Preventive  Medicine  and  Hygiene,  Har\-ard  Medical 
School,  Boston,  Mass. 

V 


VI  CONTENTS 

Page 

The  pandemic  of  1918 59 

Date  of  first  increased  prevalence  in  various  localities 65 

Influenza  in  China 80 

Autumn  spread  in  the  United  States 81 

Recrudescences 87 

Recurrences  in  the  winter  of  1919-1920 89 

The  winter  of  1920 90 

Incubation  period 95 

Predisposing  causes 96 

Periodicity • 97 

Virulence  enhancement 108 

Meteorologic  conditions 113 

Secondary  invaders 114 

Origin  of  the  1918  pandemic 116 

SECTION  III. 

An  Investigation  of  Influenza  in  Boston  (Winter  of  1920.) 127 

Diagnostic  standards  for  the  1918  epidemic 134 

Standards  for  1920 134 

Morbidity 137 

Relation  of  sex  to  morbidity 143 

Relation  of  sex  to  severity 145 

Morbidity  by  age 145 

Relationship  of  occupation  to  morbidity 150 

Effect  of  race  stock 155 

MortaUty 156 

Mortality  by  sex 165 

Relationship  to  age 167 

Relationship  of  occupation 170 

Density  of  population 170 

Race  stock  and  mortality 173 

SECTION  IV. 

An  Intensive  Study  of  the  Spread  op  Influenza  in  Small  Groups  of 

Closely  Associated  Individuals 175 

Effect  of  overcrowding 179 

Domestic  cleanliness 187 

Economic  status 189 

Distribution  of  the  disease  through  the  household 191 

The  first  case  in  the  family 194 

Intimacy  of  family  contact 197 

Recurrent  cases 198 

SECTION  V. 
Immunity 199 


CONTENTS  Vil 

SECTION  VI. 

Pack 

Influenza  and  Otiikr  Diseases 212 

IiiflucnzH  and  tuhcrculosis 212 

OtluT  infect imis  diseasos 220 

Encephalitis  letliargica 222 

SECTION  VII. 

Compauison  of  Influenza  with  Other  Epidemic  Diseases 224 

Epizootics ■ 224 

Asiatic  cholera 228 

Epidemic  meningitis 228 

Plague 229 

Measles 231 

SECTION  VIII. 

The  Prevention  and  Control  of  Influenza 234 

Ajiticipatory  or  preventive  measures 236 

Organization  of  health  services 237 

Palliative  measures  in  the  presence  of  an  epidemic 239 

Problems  for  the  future.     Constructive  research 241 

Bibliography 245 


Digitized  by  the  Internet  Archive 

in  201D  with  funding  from 

Open  Knowledge  Commons 


http://www.archive.org/details/influenzaepidemiOOvaug 


INFLUENZA. 
AN  EPIDEMIOLOGIC  STUDY. 

SECTION  I. 

General  Epidemiologic  Considerations. 

Those  who  seek  to  find  in  a  study  of  the  epidemiology  of  epidemic 
influenza  the  secret  of  the  causation  of  the  disease,  and  its  ultimate 
eradication,  are  probably  predestined  to  at  least  partial  failure.  We 
must  call  upon  the  bacteriologist  for  information  as  to  the  causative 
organism,  and  in  time  he  may  be  able  to  furnish  us  with  satisfactory 
prophylactic  measures,  particularly  with  a  successful  vaccine. 

But  while  pure  epidemiologic  studies  will  not  demonstrate  the 
ultimate  factor  in  the  etiology,  nevertheless  these  studies  do  subserve 
several  most  important  functions.  The  bacteriologist,  the  immunolo- 
gist,  the  serologist  have  accumulated  a  wealth  of  information  since 
the  1918  pandemic,  but  as  far  as  definite  conclusions  concerning  the 
causative  agent  of  the  disease  are  concerned  we  are  no  nearer  to  the 
truth  than  we  were  at  the  time  when  Pfeiffer  made  his  original  ob- 
servations. There  is  no  incontrovertible  evidence  by  which  one  may 
say  that  the  influenza  bacillus  is  or  is  not  the  cause  of  the  disease.  We 
must  therefore  await  further  studies  and  future  discoveries.  But 
we  cannot  await  idly  in  the  knowledge  that  new  epidemics  of  the 
dread  disease  will  surely  come,  probably  mild  ones  in  the  next  few 
years,  and  certainly  severe  ones  again  within  a  few  decades.  We 
must  amass  all  of  the  available  information  concerning  the  mode  of 
action  of  the  disease,  its  maner  of  spread,  its  degree  of  infectivity,  its 
distribution  and  the  mode  of  its  recurrences,  and  try  to  formulate 
from  a  study  of  the  available  facts  some  means  of  protecting  ourselves 
against  the  epidemic,  if  not  of  preventing  it  entirely. 

In  short,  in  the  present  state  of  the  bacteriologic  knowledge  of  the 
disease,  we  may  say  that  the  epidemiologic  features  are  the  only  facts 
upon  which  we  have  to  build  in  planning  our  defense.  Today,  the 
practical  work  in  the  eradication  of  influenza  must  depend  chiefly,  if 
not  solely,  on  the  general  methods  of  preventive  medicine. 

1 


Z  INFLUENZA 

Many  valuable  monographs  have  been  written  on  the  subject, 
particularly  following  the  pandemic  of  1889-1893,  but  these  have  all 
emphasized  features  and  phases  of  the  disease  which  seemed  at  that 
time  to  be  particularly  important.  Facts  which  seemed  of  extreme 
importance  to  the  earlier  writers  are  today  in  some  instances  considered 
relatively  imimportant,  while  other  phenomena  which  were  but 
touched  upon  by  the  former  investigators  today  have  assumed  deep 
significance.  For  this  reason  it  is  worth  while  to  reproduce  here  the 
observations  made  in  previous  epidemics,  and  to  correlate  them  with 
the  facts  developed  in  the  abundant  literature  of  the  last  few  years, 
and  to  draw  therefrom  inferences  as  to  the  life  and  habits  of  the  in- 
fluenza virus,  and  conclusions  as  to  the  means  of  interrupting  its 
progress. 

Historical. 

The  history  of  influenza  can  justly  be  divided  into  two  phases,  the 
first  ancient,  and  the  second  modern.  The  latter  period  begins 
with  the  1889  pandemic.  By  that  time  the  science  of  bacteriology 
had  altered  our  concepts  of  the  etiology  of  disease  and  epidemiologists 
had  begun  to  avail  themselves  of  statistical  methods  of  analysis. 
For  the  purposes  of  this  paper,  therefore,  consideration  will  be  given 
ohiefly  to  the  epidemic  of  1889,  and  a  summary  of  earlier  epidemics 
will  be  made  merely  to  refresh  our  minds  concerning  the  antiquity  of 
the  disease  and  the  periods  of  its  occurrence.  References  to  the 
earlier  epidemics  will  be  made  more  particularly  in  the  special  discus- 
sions later,  where  points  of  similarity  or  difference  will  be  brought  out. 
Further  than  that  it  is  unnecessary  to  go  in  the  history  of  the  disease, 
for  the  several  excellent  monographs  of  1890  to  1900  tell  the  historical 
story  in  a  manner  that  could  scarcely  be  improved  upon. 

The  great  antiquity  of  epidemic  influenza  is  a  fact  which  I  think 
may  be  admitted  in  spite  of  some  who  hesitate  to  accept  it  because  of 
lack  of  convincing  descriptive  evidence.  Some  believe  that  the 
epidemic  of  the  year  412  B.C.,  described  by  Hippocrates  and  by  Livy, 
was  an  epidemic  of  influenza.  Some  have  suggested  that  the  epidemic 
described  by  Thucydides  was  the  same  disease.  Parkes  remarks 
that  the  epidemic  pervading  the  Athenian  Army  in  Sicily  in  415  B.C., 
recorded  by  Diodorus  Siculus,  has  been  supposed  to  have  been  influ- 
enza. Finkler,  in  referring  to  a  report  by  Diodorus  of  a  pestilence 
occurring  in  395  B.C.,  which  broke  out  in  the  Greek  Army  at  the  siege 
of  Syracuse,  and  which  killed  off  the  soldiers  murderously,  says  that 
this  could  not  have  been  influenza.  He  regards  as  sufficient  argument 
the  fact  that  the  mortality  was  high.     After  the  epidemic  of  1918,  one 


AN    EPIDEMIOLOniC    STX'DV  3 

is  more  inclined  to  believe  tluit  the  epidemic  in  Sicily  may  well  have 
been  true  influenza.  We  must  remember  that  previous  to  the  last 
few  pandemics  the  stories  have  been  fragmentary  in  character  and 
were  told,  not  by  physicians,  but  chietly  by  the  historians  of  the  time, 
men  who  have  desired  to  impress  their  readers  with  some  idea  of  the 
horrible  ravages  of  the  disease,  and  who  have  doubtless  in  some  in- 
stances transmitted  the  impression  of  monstrous  mortality  rates.  The 
early  historians  were  nmch  given  to  figures  of  speech,  many  of  which 
were  very  telling  in  conveying  the  impression  desired.  Finally,  the 
writers  of  the  middle  ages  and  of  earlier  times  had  little  or  no  statistical 
material  on  which  to  base  their  conclusions.  I  have  no  doubt  that 
a  historian  who  during  the  1918  epidemic  of  influenza  might  have 
limited  his  observations  entirely  to  the  disease  as  it  occurred  at  Camp 
Sherman,  Ohio,  and  who  saw  125  robust  soldiers  dying  each  day, 
would  have  truly  written  that  the  disease  killed  off  the  soldiers  murder- 
ously. A  further  statistical  argument  in  favor  of  considering  the 
epidemic  among  the  Greek  soldiers  as  quite  possibly  influenza  is  the 
fact  that  as  shown  by  present  day  findings  these  men  were  all  of  the 
age  in  which  the  mortality  is  highest,  and  were  living  under  sanitary 
conditions  which  predispose  to  high  incidence  and  high  mortality. 

According  to  Parkes,  in  827  A.D.,  an  attack  of  ''cough"  which 
spread  like  the  plague  was  recorded.  In  876,  Italy  and  later  the  whole 
of  Europe  was  attacked,  and  the  army  of  Charlemagne,  returning 
from  Italy,  suffered  greatly.  "Dogs  and  birds  were  attacked  at  this 
time."  In  976  the  whole  of  France  and  Germany  was  attacked  by  a 
fever  whose  principal  symptom  was  cough.  There  is  also  record  of 
diseases  which  may  have  been  influenza  which  were  seen  in  Germany 
and  France  in  927  and  in  England  in  996  and  997.  All  of  these  records 
are  indefinite  and  from  their  nature  unconvincing  to  a  critical  student. 
Several  investigators  have  gone  over  these  past  records  up  to  1889 
with  the  idea  of  determining  definitely  what  plagues  were,  and  which 
were  not,  true  influenza.  The  criteria  used  by  the  various  investiga- 
tors have  differed  slightly  in  some  instances.  For  instance,  one 
chooses  to  use  the  record  of  low  mortality  in  widespread  epidemics  as 
the  chief  characteristic  of  pandemic  influenza,  while  another  empha- 
sizes principally  the  complications. 

The  experience  of  recent  years  has  amplj^  demonstrated  that 
influenza  may  be  characterized  by  a  high  mortality  or  a  low  mortality; 
that  pneumonia  may  be  prevalent  or  relatively  rare  during  an  epi- 
demic. These  features  are  not  truly  characteristic  of  influenza  itself. 
They  are  phenomena  which  depend  chiefly  for  their  existence  on 
secondary  invasion  with  organisms  other  than  the  causative  agent  of 


4  INFLUENZA 

influenza.  It  may  be  that  the  influenza  virus  itself  is  capable  of 
producing  pneumonia,  but  it  is  generally  accepted  that  an  overwhelm- 
ing majority  of  the  complicating  pneumonias  are  due  to  secondary 
infections.  One  perusing  the  former  literature  today  would  hesitate 
to  state  that  an  ancient  epidemic  was  not  influenza  merely  because 
it  was  accompanied  by  high  mortality,  nor  would  he  wish  to  say  that 
it  was  not  this  disease  because  there  was  no  mention  of  a  high  incidence 
of  pneumonia.  We  have  had  both  types  within  the  last  few  years, 
as  in  March  and  April,  1918,  when  the  disease  appears  to  have  been 
accompanied  by  a  very  low  mortality  and  a  low  incidence  of  pneumo- 
nia, and  in  October  of  the  same  year  when  the  pneumonia  incidence 
and  the  death  rate  were  both  relatively  much  higher. 

Attention  should  be  called  to  a  certain  inaccuracy  which  has 
appeared  in  the  literature  and  which  has  resulted  in  some  instances  in 
a  misunderstanding  of  the  entire  history  of  influenza.  Finklersays: 
"According  to  August  Hirsch  the  first  influenza  epidemic  occurred  in 
1173  and  he  places  it  in  his  work  as  the  first  out  of  eighty."  This 
has  given  the  impression  to  some  that  influenza  was  unknown  previous 
to  that  date.  Leichtenstern  has  quoted  Hirsch  more  accurately  and 
thereby  given  an  entirely  different  meaning  to  the  statement.  Au- 
gust Hirsch  says  that  the  first  epidemic  that  can  be  definitely  said  to 
be  influenza  occurred  in  1173."  Jordan  also  conveys  the  latter 
impression.  He  remarks  that  the  first  extensive,  well  described 
epidemic  of  influenza  occurred  in  1510. 

Hirsch  places  the  first  authoritative  influenza  epidemic  in  the  year 
1173;  Zeviani  in  1293;  Gluge  in  1323;  Schweich,  Biermer  and  Rip- 
perger  in  1387;  while  Saillant,  Thompson,  Zuelzer  and  Leichtenstern 
accept  nothing  prior  to  the  first  pandemic  of  1510  as  being  unquestion- 
ably influenza.  It  should  be  remarked  here  that  opinion  is  not  un- 
animous in  every  case  as  to  the  identity  of  all  epidemics  following  1510. 

Hirsch  concluded  that  there  have  been  about  eighty  epidemics 
since  that  of  1173.  Parkes  states  that  in  the  fourteenth  century  there 
were  six  epidemics,  in  the  fifteenth  seven,  in  the  sixteenth  eleven,  in 
the  seventeenth  sixteen,  in  the  eighteenth  eighteen,  while  in  the  first 
half  of  the  nineteenth  ten  epidemics  are  on  record. 

Table  I  shows  in  brief  review  the  occurrence  of  the  more  important 
epidemics  since  the  year  1173.  Like  all  similar  summaries  given  in 
tabular  form  it  possesses  the  disadvantage  of  telHng  only  parts  of  the 
entire  story,  and  those  in  only  a  very  general  way,  but  it  will  suffice 
as  a  resume  and  for  the  emphasis  of  certain  phenomena  to  which  at- 
tention will  be  later  directed. 

Concerning  the  epidemic  of  1889,  it  is  usually  stated  that  it  had  its 


AX    EPIDEMIOLOfMC    .STUDY  ft 

origin  in  Bokliam  in  May  of  that  year.  As  will  be  sc(mi  from  the  table 
influenza  was  present  also  in  Greenland  and  tiie  Hudson  Hay  territory 
in  the  spring  of  1889.  The  possibility  of  simultaneous  origin  in  at 
least  two  localities  in  that  year  will  be  diseussed  later.  The  epidemic- 
remained  in  Bokhara  until  August  of  the  same  year,  after  which  time 
it  slowly  traveled  to  Siberia  where  at  Tomsk  traces  of  the  disease 
were  observed  with  ceitainty  in  October.  At  that  time  it  was  also 
observed  in  the  Caucasus  and  in  European  Russia.  It  appeared  in 
Petrograd  in  October,  1889,  and  remained  epidemic  until  Deceml>er 
of  that  year.  The  spread  of  this  epidemic  throughout  the  world  is 
indicated  in  the  following  table  adopted  from  Leichtenstern: 

Spread  of  Influenza  in  1889-90. 


Month.  1889-90. 


First  (October") St.    Petersburg,    Moscow,   Courland,  Livonia 

Finland. 

Second Berlin,  Paris,  Vienna,  Sweden,  Denmark. 

Third London,    Holland,    Belgium,    Balkan    States, 

North  America. 

Fourth Capetown,  Egypt.  Honolulu,  Mexico,  Japan, 

Hong-Kong. 

Fifth San   Francisco,    Buenos   Aires,    India,    Sierra 

Leone,  Scilly  Islands. 

Sixth Chili,  Kamerun,  Zanzibar,  Basutoland,  Tas- 
mania. 

Seventh British  Bechuanaland,  Barbados. 

Eighth Gold  Cost,  Natal. 

Ninth Trinidad. 

Tenth Iceland,  Madagascar,  China,  Senegal. 

Eleventh Kashmir,  Katunga. 


Between  the  years  1889  and  1893  according  to  Leichtenstern  there 
was  no  period  altogether  free  from  influenza.  Here  and  there  in- 
dividual cases  or  small  epidemics  sharplj^  localized  were  observed.  In 
1893  another  epidemic  appeared  in  many  places  and  became  quite 
widespread.  There  was  not,  according  to  this  author,  the  definite 
geographic  progression  that  had  been  observed  in  1889.  This  was 
but  a  recrudescence,  a  lighting  up  from  endemic  foci  remaining  after 
the  first  wide  spread.  In  the  first  half  of  1893  there  was  a  light  spring 
epidemic,  and  in  November  of  the  same  year  a  larger  epidemic  swept 
over  the  whole  of  Europe.  The  height  of  the  latter  was  reached 
chiefly  in  December. 

The  influenza  incidence  subsequent  to  1893  will  be  discussed  later. 


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12  INFLUENZA 

Table  I  shows  that  prior  to  1510  the  information  was  so  limited  as 
to  be  not  entirely  conclusive.  We  must  rely  upon  the  fragmentary 
descriptions  of  writers  located  usually  in  or  near  the  intellectual  centers 
who  described  the  disease  as  they  saw  it  in  their  city  or  country.  We 
have  no  way  of  ascertaining  what  other  countries  were  invaded,  and 
we  possess  no  method  by  which  we  may  enumerate  the  "silent  areas, " 
countries  which  in  the  absence  of  a  chronicler  have  not  been  able  to 
transmit  their  story. 

There  have  been  fourteen  very  widespread  epidemics  since  1510, 
all  of  which  might  appropriately  be  designated  as  pandemics.  They 
are  those  of  1510,  1557,  1580,  1593,  1729,  1732,  1762,  1782,  1788,  1830, 
1833,  1836,  1847,  1889  and  1918.  Some  of  these  have  spread  farther 
than  others  according  to  the  records,  but  in  nearly  all  we  have  reports 
of  influenza  being  present  in  practically  every  country  provided  with 
a  historian.  We  may  find  from  the  table  another  group  in  which 
there  have  been  more  or  less  extensive  epidemics,  apparently  related, 
but  without  any  general  direction  of  spread.  Such  are  the  epidemics 
of  1709-12,  1757-67,  1802-03,  1838-47  and  the  period  1850-59. 
Finally,  there  are  at  least  ten  periods  during  which  relatively  small 
areas  have  been  affected  with  epidemic  influenza.  Such  for  instance 
is  the  year  1688  when  the  disease  was  apparently  localized  in  Great 
Britain  and  Ireland;  in  the  year  1693  when  England  and  the  adjacent 
continent  were  involved,  with  little  spread  elsewhere;  and  again  in 
1742,  when  there  was  a  slow  spread  through  Germany  into  adjacent 
countries  with  recurrences  in  the  former  up  until  1745. 

In  England  the  following  epidemics  have  been  recorded,  some  of 
them  in  great  detail:  1510  and  1557,  described  by  Thomas  Short; 
1658  by  Willis;  1675,  by  Sydenham;  1729-1743  by  Huxham;  1732-33 
by  Arbuthnot;  1758  by  Whytt;  1762  by  Baker  and  Rutty;  1767  by 
Heberden;  1775  by  Fothergill,  who  collected  observations  from  many 
physicians;  in  1782  by  Gray,  Haygath  and  Carmichael  Smith;  1803  by 
Pearson  and  Falconer,  and  a  great  number  of  others;  1833  by  Hinges- 
ton  and  others;  1837  by  Streeten,  Graves,  and  Bryson,  etc.;  1847  by 
Peacock,  Laycock  and  many  others;  also  those  of  1855  and  1889-93. 

According  to  Stallybrass,  epidemic  crests  have  been  reached  in 
England  in  1789-90,  1802-03,  1830-32,  1840-41,  1848-51,  1854, 
1869-70,  1879,  1890-91,  1898  and  1918  to  1920.  The  periodicity  in 
multiples  of  ten  years  in  this  latter  group  is  remarkable. 

The  disease  appears  to  have  visited  North  America  in  the  years 
1627,  1647,  1729,  1732,  1737,  1762,  1782,  1789,  1811,  1832,  1850,  1857, 
1860,    1874,    1879,    1889,    1900,    1915-1916    and    1918-20.     Abbott 


A.\    EPIDEMIOLOGIC    STUDY  13 

speaks  particularly  of  the  years  1G47,  ICoo  ami  1097-98,  1732,  1762 
and  1782  and  1889  as  being  years  of  especial  epidemic  prevalence  in 
this  country. 

Clinical  and  Epidemiologic  Identification. 

Up  to  the  present  time  we  have  discovered  no  one  characteristic 
bj-  which  we  may  say  that  a  case  or  an  epidemic  is  positively  influenza. 
We  have  had  to  rely  on  the  general  symptomatology,  which  indeed 
is  suflBciently  characteristic,  although  so  nearly  like  the  symptoms  of 
certain  other  diseases  as  to  make  us  hesitate  to  make  an  absolute 
diagnosis,  and  on  the  epidemic  characteristics.  The  necessity  of  an 
absolute  criterion  in  the  clinical  diagnosis  is  particularly  felt  in  the 
presence  of  an  isolated  interepidemic  case,  or  a  small  endemic  out- 
break. It  ie  at  this  point  that  the  opinions  of  epidemiologists  diverge, 
a  divergence  which  results  in  two  schools  of  thought  in  the  explanation 
of  the  endemic  source  of  epidemic  influenza.  Are  the  interepidemic 
cases  and  the  small  localized  epidemics  due  to  the  virus  which  causes 
the  great  pandemics;  are  they  influenza  vera,  or  are  they  entirely 
different  diseases  with  similar  S3"mptomatology,  caused  b}'  some  other 
microorganism  and  should  they  be  designated  by  some  other  name? 
Thus  Leichtenstem  remarks:  "When  we  go  over  the  records  of  the 
yeais  1173  to  1875,  and  particularly  those  of  the  last  century,  when 
the  information  has  been  more  extensive  and  more  accurate,  we  find 
that  scarcely  a  year  has  passed  without  news  of  the  epidemic  occur- 
rence of  influenza  at  some  point  or  other  of  the  earth.  Some  of  these 
local  and  territorial  epidemics  are  merely  endemic  recurrences  of  the 
great  pandemics  which  have  left  the  germ  deposited  in  the  various 
localities.  Others  of  these  small  epidemics  probablj'  have  nothing 
to  do  with  influenza  vera,  but  are  local  outbreaks  of  catarrhal  fever." 

Contrary  to  the  usual  belief,  influenza  is  a  disease  of  quite  definite 
and  distinct  characteristics,  both  clinical  and  epidemiological.  The 
symptoms  are  clear  cut,  with  sudden  onset,  severe  prostration  out  of 
all  proportion  to  the  clinical  symptoms  and  to  the  fever,  headache 
and  pain  in  the  back,  general  body  pains,  and  fever  of  greater  or  less 
degree.  There  is  usually  a  lack  of  leucocytosis  or  a  true  leucopenia. 
In  uncomplicated  influenza  there  aie  as  a  rule  no  localizing  symptoms. 
There  may  be  a  slight  soreness  of  the  throat,  or  a  slight  cough,  but 
these  are  at  best  mild.  The  fever  lasts  from  thiee  to  five  days  and 
disappears,  while  at  the  same  time  all  of  the  symptoms  clear  up  with 
the  exception  of  the  profound  prostiation,  which  as  a  rule  continues 
for  some  time,  rendering  convalescence  surprisingly  slow.     The  pain 


14  INFLUENZA 

in  the  back  may  remain  for  a  week  or  so.  This  is  the  description  of 
uncomplicated  influenza. 

The  manner  of  spread  of  epidemic  influenza  is  constant  in  a  primary 
epidemic  and  the  epidemic  as  a  whole  has  certain  features  which 
render  it  characteristic.  The  sporadic  case  has  as  a  rule  the  same  quite 
clear  cut  clinical  symptomatology,  but  it  fails  to  manifest  the  one 
feature  most  characteristic  of  epidemic  influenza — a  high  degree  of 
contagiousness.  Further,  although  the  symptoms  in  themselves  are 
characteristic,  there  is  no  one  pathognomonic  sign  by  which  one  may 
say,  "this  is  a  case  of  influenza,"  and,  finally  other  disease  conditions 
such  as  tonsillitis,  frequently  resemble  it  so  much  as  to  cause  error  in 
diagnosis. 

This  becomes,  then,  one  of  the  problems  in  the  study  of  influenza 
epidemiology.  It  is  a  matter  of  first  importance  to  determine  once 
and  for  all  whether  true  influenza  is  with  us  always,  or  whether  it 
appears  only  at  the  time  of  the  great  pandemics.  Upon  the  answer  to 
this  question  more  than  upon  any  other  one  thing  rests  our  choice  of 
methods  of  eradication.  Any  procedures  of  preventive  medicine  that 
may  be  undertaken  on  the  assumption  that  the  source  of  pandemic 
influenza  is  to  be  found  in  one  or  a  few  endemic  foci,  such  as  the  one 
supposed  to  exist  in  Turkestan,  would  fail  utterly  should  the  true 
condition  be  that  of  a  universal  distribution  of  a  relatively  avirulent 
virus  which  from  time  to  time  from  some  unknown  cause  assumes  a 
highly  increased  virulence. 

Before  becoming  involved  in  this  very  complicated  question,  let 
us  familiarize  ourselves  completely  with  the  characteristics  of  the 
pandemic  and  epidemic  variety  of  the  disease. 

General  Characteristics   of  Early  Epidemic   Outbreaks. 

We  have  described  the  symptomatology  of  uncomplicated  influenza. 
It  is  rare  that  this  clinical  picture  is  seen  alone  during  the  height  of 
an  epidemic.  Complications,  chiefly  of  the  respiratory  tract,  as  a  rule 
occur  in  such  a  large  proportion  of  individuals  that  they  very  nearly 
dominate  the  picture.  Although  caused  by  various  micro-organisms, 
all  of  which  appear  to  be  secondary  factors  the  results  are  so  character- 
istic that  in  the  past,  descriptions  of  influenza  epidemics  have  usually 
been  descriptions  of  the  complications  of  epidemic  influenza.  Most 
influenza  epidemics  are  complicated.  But  we  do  know  from  the 
experience  of  recent  years  as  well  as  from  history  that  relatively 
uncomplicated  epidemics  of  influenza  have  occurred,  and  that  when 


AX    ElMDKMIOLO(;i('    STLDY  15 

they  do  so  occur  u,  prcdoniinunl  characteristic  has  been  the  extreme 
mildness. 

It  is  a  fundaniontal  characteristic  of  pandemic  influenza  that 
early  cases  in  widespread  epidemics,  as  well  as  in  "pre-ejjidemic 
increases"  are  very  mild,  with  a  minimum  of  lespiratory  complications 
and  with  exceedingly  low  mortality.  It  is  because  we  are  better 
acquainted  with  the  more  severe  variety  that,  when  these  mild  pre- 
cursors appear  we  are  always  in  doubt  for  a  time  as  to  their  true 
identity. 

In  spite  of  our  20th  century  erudition,  the  influenza  when  it  first 
appeared  in  mild  form  in  the  American  Expeditionary  Forces  in  1918, 
for  a  lack  of  better  knowledge  as  to  its  cause  was  called  "three-day 
fevei."  In  Italy  in  the  same  year  the  designation  of  the  disease  pro- 
gressed from  pappataci  fever  through  "Spanish  grip"  and  "summer 
influenza,"  until  finally  it  was  designated  influenza,  pure  and  simple. 
Sampietro  in  Italy  particularly  discussed  the  possibility  of  the  disease 
being  pappataci  fever. 

Belogu  and  Saccone,  who  wrote  in  May  of  1918,  decided  that  the 
epidemic  was  not  influenza  in  spite  of  the  manifest  clinical  similarity, 
chiefly  because  of  the  absence  of  signs  of  secondary  invasion,  such  as 
nervous  symptoms,  gastro-intestinal  symptoms,  and  pneumonia,  and 
especially'  because  of  the  rapid  recovery  after  defervescence.  They  also 
considered  the  possibility  of  pappataci  fever  and  dengue,  and  ruled 
out  both.  They  discussed  calling  the  condition  "influenza  nostras," 
but  reached  no  definite  conclusion.  Trench  fever  was  also  considered 
by  some.  United  States  Public  Health  Reports  for  1918  record  that 
dengue  was  reported  prevalent  at  Chefoo,  China,  during  the  two  weeks 
ended  June  15th,  1918.  One  week  later  there  was  a  paragraph  stating, 
''Prevalence  of  a  disease  resembling  dengue  and  affecting  about 
fifty  per  cent,  of  the  population  was  reported  at  Shanghai,  China, 
June  15,  1918."     It  is  not  impossible  that  this  was  influenza. 

Zinsser  reminds  us  that  Hayf elder,  when  he  saw  the  influenza  as 
it  spread  in  Petrograd  in  November  of  1889,  remarked  its  close  clinical 
similarity  to  the  description  of  an  epidemic  of  dengue  which  had 
prevailed  in  Constantinople  during  the  preceding  September.  Hay- 
felder,  in  studying  the  1889  epidemic  at  its  onset  in  Russia  and  the 
East,  wrote  of  "Sibirisches  Fieber"  which  was  first  looked  upon  as 
malaria  owing  to  the  apparently  complete  absence  of  the  compUcating 
lesions  habitually  associated  in  our  minds  with  influenza. 

The  same  difficulty  in  early  identification  was  experienced  in  this 
country  in  1918.     At  the  end  of  March  of  that  year  the  author  who 


16  INFLUENZA 

was  stationed  at  Camp  Sevier,  South  Carolina,  was  one  of  a  Board  of 
Officers  appointed  to  investigate  a  disease  which  had  broken  out  among 
troops  stationed  at  that  camp.  At  that  time  the  b'ne  troops  consisted 
of  three  infantry  regiments  and  three  machine  gun  battaKons.  On  the 
day  following  a  parade  in  the  city  of  Greenville  a  considerable  number 
of  men  in  three  out  of  the  six  organizations  suddenly  took  ill.  There 
were  a  few  isolated  cases  in  other  organizations,  but  in  the  one  infantry 
regiment  and  two  machine  gun  battalions  the  regimental  infiimaiies 
weie  filled,  and  some  cases  were  sent  to  the  base  hospital.  Nearly  all 
were  very  mildly  ill  and  exhibited  the  symptoms  of  pure  uncomplicated 
influenza  as  described  above.  The  onset  was  sudden,  there  were  the 
usual  pains  and  aches,  the  bowels  were  regular,  there  was  a  feeling  of 
discomfort  in  the  pit  of  the  stomach  in  many  instances,  and  there  were 
no  sore  throats  and  very  little  cough.  Recovery  was  as  a  rule  very 
rapid,  although  about  a  dozen  of  the  entire  number  developed  pneu- 
monia and  some  of  these  died.  Physical  examination  of  those  only 
mildly  ill  and  who  remained  in  the  regimental  infirmary  showed  as  a 
rule  nothing,  but  in  some  instances  scattered  fine  moist  rales  near  the 
hilus  of  the  lungs.  In  some  of  the  organizations  the  disease  was 
definitely  spread  down  rows  of  company  tents.  Careful  bacteriologic 
examination  was  made  at  the  time  and  the  predominating  organisms 
were  found  to  be  a  gram-negative  coccus  resembhng  micrococcus 
catarrhalis,  and  a  non-hemolytic  streptococcus.  This  was  in  uncompli- 
cated cases. 

The  Board  decided  that  the  disease  should  be  called  influenza, 
but  our  only  basis  for  such  decision  were  the  clinical  symptoms  and 
the  contagious  character.  At  that  time  none  of  us  dreamed  of  any 
possible  connection  with  a  severe  epidemic  to  occur  later,  and  labora- 
tory search  for  influenza  bacilli  which  was  carefully  made  in  view  of 
the  chnical  diagnosis  showed  none  of  these  organisms  to  be  present. 

At  about  the  same  time  a  similar  epidemic  was  being  experienced 
at  Fort  Oglethorpe,  Ga.  V.  C.  Vaughan,  in  describing  this  epidemic, 
remarks:  "A  disease  strongly  resembling  influenza  became  prevalent 
in  the  Oglethorpe  Camp  about  March  18,  1918.  It  soon  assumed 
pandemic  proportions.  Within  two  weeks  every  organization  in  Camp 
Forrest  and  the  Reserve  Officers  Training  Camp  was  affected. 

"The  symptoms  were  as  follows:  Headache,  pain  in  the  bones  and 
muscles,  especially  the  muscles  of  the  back,  marked  prostration,  fever, 
sometimes  as  high  as  104  degrees.  Someiimes  there  was  conjunctivi- 
tis, coryza,  a  rash  and  possibly  nausea,  recovery  taking  place  in  a 
few  days. 


AN    EPIDEMIOLOGIC    STUDY  17 

"In  all  organizations  the  epidemic  was  first  located  in  conipanics 
before  it  became  general. 

"The  incubation  period  was  short,   not  over  one  or  two  days. 

"Some  organizations  suffered  more  than  others  for  no  apparent 
reason. 

"It  is  probable  that  the  epidemic  disease  was  recently  broufrhl  to 
these  camps.  If  it  is  genuine  influenza,  and  the  epitiemiological 
features  no  less  than  the  leading  symptoms  seem  to  point  to  that 
disease,  there  is  here  offered  the  most  reaf-onable  explanation  of  the 
outbreak  w^hich  is  now  possible.  No  other  disease  spreads  so  fast  or 
is  so  prostrating,  considering  its  symptoms." 

We  will  quote  at  some  length  from  the  report  of  Zinsser  of  the 
Chaumont  epidemic  in  France  in  1918,  because  of  the  excellence  of  the 
description,  and  particularly  because  Zinsser  has  followed  three 
successive  epidemics  with  successive  increases  in  the  complications 
and  corresponding  transformations  in  the  clinical  picture.  It  is 
worthy  of  special  note  that  he  has  remarked  that  the  influenza,  as 
first  seen  at  Chaumont,  showed  nothing  in  the  symptoms  that  would 
suggest  a  predominant  respiratory  tract  infection. 

"It  will  be  useful  to  discuss  briefly  the  early  cases  as  we  saw  them 
during  the  Chaumont  epidemic,  not  because  the  observations  made 
there  add  much  that  is  new  from  a  clinical  point  of  view,  but  because 
they  will  remove  any  possible  ambiguity  concerning  our  conception 
of  influenza  in  its  pure  uncomplicated  form. 

"As  far  as  we  can  judge  the  httle  outbreak  at  headquarters  was 
typical  of  the  first  advent  of  epidemic  influenza  in  many  places.  The 
population  of  the  town,  at  the  time,  consisted  of  a  large  office  personnel 
attached  to  the  military  administration,  scattered  as  to  billets  and 
places  of  work;  of  military  units  living  in  barracks  and  eating  at  com- 
mon messes;  and  of  the  townspeople.  The  epidemic  descended  upon 
individual  military  units  with  the  suddenness  of  a  storm,  striking  a 
considerable  percentage  of  the  men,  perhaps  most  of  the  susceptible 
material,  within  less  than  a  week,  and  ending  almost  as  abruptl}^ 
with  only  a  few  isolated  cases  trailing  behind.  Among  the  more 
scattered  oflice  workers  and  among  the  townspeople  it  was  dissemi- 
nated more  gradually  and  trailed  along  for  a  longer  period. 

"These  early  cases  were  clinicalh'  so  uniform  that  a  diagnosis 
could  be  made  from  the  history  alone.  The  onset  was  almost  uni- 
formly abrupt.  Typical  cases  would  become  ill  suddenl}^  during  the 
night  or  at  a  given  hour  in  the  day.  A  patient  who  had  been  per- 
fectly well  on  going  to  bed,  would  suddenly  awake  with  a  severe 


18  INFLUENZA. 

headache,  chilliness,  malaise  and  fever.  Others  would  arise  feeling 
perfectly  well  in  the  morning,  and  at  some  time  during  the  day  would 
become  aware  of  headache  and  pains  in  the  somatic  muscles. 

"The  typical  course  of  these  cases  may  be  exemplified  by  that  of 
J.  T.  W.,  a  draftsman  attached  to  the  29th  Engineers.  He  was 
perfectly  well  until  May  20th,  working  regularly,  his  bowels  and 
appetite  normal,  considering  himself  healthy.  On  May  21st,  at 
4 :30  A.M.  he  awoke  with  a  severe  headache.  He  arose,  forced  himself 
to  eat  breakfast  and  tried  to  go  to  work.  He  began  to  feel  feverish 
and  chilly.  At  the  same  time  his  headache  became  worse,  with  pains 
in  the  back,  and  burning  in  the  eye  balls.  At  2  p.m.  he  reported  sick, 
and  was  taken  to  the  hospital  with  a  temperature  of  102.8  degrees. 
At  midnight  his  temperature  dropped  to  101.6  degrees,  and  came 
down  to  normal  by  noon  of  the  22d.  As  he  recovered  he  developed  a 
slight  sore  throat,  great  soreness  of  the  legs  and  a  very  slight  cough. 
He  recovered  completely  within  a  few  days. 

"These  eases  with  a  few  exceptions  developed  no  rashes.  One  or 
two  of  them  had  blotchy  red  eruptions  which  we  felt  incompetent  to 
characterize  dermatologically.  The  leucocyte  counts  ranged  from 
5,000  to  9,000.  A  very  few  went  above  this.  Sometimes  there  was  a 
relative  increase  of  lymphocytes,  but  this  was  by  no  means  regular. 
The  few  spinal  fluids  that  were  examined  were  normal.  As  to  en- 
largement of  the  spleen,  we  can  say  nothing  definitely. 

"Soon  after  this  we  observed  the  disease  in  a  Division,  the  42d, 
then  holding  a  part  of  the  line  in  front  of  Baccarat.  Here  it  had 
already  developed  a  somewhat  different  nature,  due,  we  believe,  to  the 
fact  that  the  men  of  this  Division  were  not,  as  were  those  at  Chau- 
mont,  living  in  a  rest  area,  but  were  actively  engaged  in  military  opera- 
tions, working,  sleeping,  and  eating  under  conditions  that  involved 
greater  fatigue,  less  protection  against  weather,  and  greater  crowding 
in  sleeping  quarters.  The  Baccarat  cases  were  much  mroe  frequently 
catarrhal;  sore  throats,  coughs  and  more  serious  respiratory  complica- 
tions were  more  common.  However,  they  were  usually  coupled 
unmistakably  with  an  underlying  typical  influenzal  attack,  sudden 
onset,  pains  and  short  lived  fever.  Moreover,  there  were  a  great 
many  of  the  entirely  uncomplicated  cases  interspersed  with  the 
others. 

"Still  later,  in  September,  October  and  November,  respiratory 
complications  were  so  frequent  and  severe,  came  on  so  early  in  the 
disease,  and  the  pneumonia  mortality  became  so  high,  that  the  funda- 
mental identity  of  these  later  cases  with  the  early  three  day  fever 


AX    EPIDEMIOLOGIC    STIDY  10 

might  easily  luivc  hecii  lust  sight  of  b}'  ol)s('iv('rs  who  hail  not  foJNiwcd 
the  gradual  tiansformation. 

"In  consideration  of  these  facts,  it  is  aj){)areiit  that  I'tiological  or 
other  investigations  can  throw  no  light  upon  the  proljleins  of  influenza 
unless  they  are  carried  out  with  clearer  understanding  of  the  differ- 
entiation between  the  complications  and  the  basic  disease. 

"The  serious  respiratory  infections  of  the  bronchi  and  lungs  we 
can  set  down  with  reasonable  certainty  as  complications  due,  certainly 
in  the  overwhelming  majority  of  cases,  to  secondary  bacterial  invaders. 
It  is  a  matter  of  considerable  difficulty,  however,  to  know  exactly 
where  the  basic  disease  stops  and  the  complications  begin;  and  whether 
we  must  regard  the  mild  sore  throat  and  conjunctival  injection  which 
so  often  accompany  the  simple  cases  as  a  part  of  this  basic  clinical 
picture,  or  as  the  simplest  variety  of  complication.  This  is  much 
more  than  an  academic  question,  since,  as  we  shall  see,  the  bacteri- 
ological analyses  of  such  lesions  have  played  an  important  role  in 
etiological  investigations." 

Symptoms  in  Former  Epidemics. 

The  difficult}'  in  making  a  decision  in  the  presence  of  an  epidemic 
is  ver3'  similar  to  that  of  deciding  whether  the  epidemics  of  former 
times  were  in  each  case  influenza.  Some  few  have  been  recorded  in 
which  the  description  has  corresponded  fairly  well  to  that  of  primary 
uncomplicated  influenza.  Thus,  concerning  the  epidemic  of  1557  in 
Spain,  Thomas  Short  wrote  as  follows:  "At  Mantua  Carpentaria, 
three  miles  from  Madrid,  the  epidemic  began  in  August  .  .  .  There 
it  began  with  a  roughness  of  the  jaws,  small  cough,  then  a  strong  fever 
with  a  pain  of  the  head,  back,  and  legs.  Some  felt  as  though  they 
were  corded  over  the  breast  and  had  a  weight  at  the  stomach,  all  of 
which  continued  to  the  third  day  at  furthest.  Then  the  fever  went 
off,  with  a  sweat  or  bleeding  at  the  nose.  In  some  few,  it  turned  to  a 
pleurisy  or  fatal  peripneumony." 

Most  of  the  descriptions,  however,  have  been  of  a  general  character 
and  include  descriptions  of  the  complicated  periods  of  the  epidemic. 
One  of  the  more  complete  of  the  early  descriptions  was  that  by  Lobin- 
eau  in  1414,  who  wrote:  "C'etait  une  espece  de  rhume,  qui  causa  un 
tel  enrouement  que  les  chastelets  furent  obhgez  d'interrompre  leurs 
seances;  on  dormoit  peu  et  Ton  souffroit  de  grandes  douleurs  k  la  teste, 
aux  reins  et  par  tout  le  reste  du  corps;  mais  le  mal  ne  fut  mortel  que 
pour  les  vieilles  gens  de  toute  condition." 

With  this  exception  we  possess  no  very  good  or  complete  descrip- 


20  INFLUENZA 

tion  of  influenza  prior  to  the  epidemic  of  1510.  After  that  time  they 
have  as  a  rule  been  detailed  enough  to  enable  identification.  Hirsch 
bases  his  conclusions  concerning  the  year  1173  chiefly  on  the  following 
quotation:  "Sub  hisdem  diebus  uni versus  orbus  infectus  ex  aeris 
nebulosa  corruptione,  stomacho  catarrhum  causante  generalem  tus- 
sim,  ad  singulorum  perniciem,  ad  mortem  etiam  plurimorum  immis- 
sam  vehementer  expavite."  Nearly  all  that  we  have  to  go  on  in  this 
description  is  the  widespread  incidence  of  the  disease  and  the  presence 
of  respiratory  symptoms,  particularly  cough.  In  1323  the  description 
emphasizes  only  the  high  morbidity.  Thus,  Pietro  Buoninsegni  writes : 
"In  questo  anno  e  d'Agosto  fu  un  vento  pestilenzia  le  per  lo  quale 
amalo  di  freddo  e  di  f ebbre  per  alcuni  di  quasi  tutte  le  persone  in  Firenze 
e  questo  madesimo  fu  quais  per  tutta  Itaha."  The  same  author 
describes  the  epidemic  of  1327,  emphasizing  again  the  high  morbidity 
and  in  addition  the  low  death  rate:  "In  detto  anno  e  mese  fu  quasi 
per  tutto  Italia  corruzione  di  f ebbre  per  freddo;  ma  pochi  ne  morirono.'' 
Again  in  1387,  he  emphasizes  the  same  two  features. 

Pasquier,  in  writing  of  the  epidemic  of  1403  in  France,  says:  "En 
Registres  de  Parlement  on  trouve  que  le  vingt-sixieme  jour  d'avril 
1403  y  eut  une  maladie  de  teste  et  de  toux,  qui  courut  universelle- 
ment  si  grande,  que  ce  jour-la  le  Greffier  ne  ptit  rien  enregistrer  et 
fut-on  contraint  d'abandonner  le  plaidoye."  Here  the  high  morbidity 
and  the  symptoms,  particularly  cough  and  pain,  are  emphasized.  In 
1414,  Baliolanus  describes  again  the  high  morbidity  and  symptoms, 
particularly  cough  and  hoarseness :  "Eoque  frigore  humanis  corporibus 
concepto  .  .  .  tussis  maxima  atque  raucitas  orta  unde  nullus  pene 
ordo,  aetas  et  sexus  liber  evasit."  In  1411,  Pasquier  writes  the  follow- 
ing: "En  1411  y  eut  une  autre  sorte  de  maladie  dont  une  infinite  de 
personnes  furent  touchez,  par  laquelle  Ton  perdoit  le  boire,  le  manger  et 
le  dormir  .  .  .  toujours  trembloit  et  avec  le  estoit  si  las  et  rompu 
que  Ton  ne  I'osoit  toucher  en  quelques  parts.  Sans  qu'aucune 
personne  en  mourut." 

Subsequent  to  1510  descriptions  have  been  as  a  rule  more  definite. 
There  are,  however,  exceptions  to  this  statement  and  these  fall  in  the 
epidemics  concerning  which  there  is  some  dispute. 

Manner  of  Spread. 

More  characteristic  and  more  important  from  an  epidemiologic 
standpoint  than  the  symptomatology  in  general,  as  we  have  discussed 
it,  is  the  mode  of  development  of  the  epidemic  as  a  whole. 


AN     KPIOli.MIOLOClC    STUDV  21 

Human  intercourse. — Before  the  days  of  Wacteriology  the  conta- 
giousness of  the  disease  was  Httle  discussed.  Its  infectiveness  was  in 
fact  not  universally  established  until  the  epidemic  of  1889-1890.  One 
of  the  first  writers  who  attempted  to  see  in  the  influenza  a  contagious 
disease  was  Ch.  Calenus  who  wrote  in  1579:  "ContaKiosum  dico 
morbum,  quia  etsi  quidem  al)  occulta  quadam  coeli  influent ia,  princi- 
paliter  eum  profisci  haud  dubium  est  .  .  .  eo  in  loco  quo  jam 
grassabatur  inter  homines  citius  eos  invadabat,  qui  cum  affectis  fre- 
quenter conversai)antur,  quam  eos,  qui  a  consuetudine  affectorum 
studiose  abstinebant."  This  keen  observer  saw  that  those  who 
carelessly  exposed  themselves  to  close  contact  with  cases  of  influenza 
were  more  likely  to  develop  the  disease  than  those  who  protected 
themselves  in  every  way  possible.  The  "contagious"  school  first 
developed  in  England,  where  Haygarth,  Hamilton,  Gray,  Hull, 
Duggard,  Bardsle3%  and  others,  in  1775-1803  described  the  disease  a? 
being  not  in  the  air,  but  in  a  specific  contagion.  Others  who  considered 
influenza  a  contagious  disease  were  Simonin,  Lombard,  Petit  deCorbeil 
(1837),  Blanc  (1860),  and  Bertholle  (1876). 

Watson  (1847)  quotes  Cullen  as  saying  that  this  species  of  catarrh 
proceeds  from  contagion.  He,  himself,  is  not  convinced  of  this  fact. 
He  says  the  visitation  is  too  sudden  and  too  widely  spread  to  be  capable 
of  explanation  in  that  way.  "There  are  facts  in  the  history  of  in- 
fluenza which  furnish  a  strong  presumption  that  the  exciting  cause 
of  the  disorder  is  material,  not  a  mere  quality  of  the  atmosphere ;  and 
that  it  is  at  least  portable.  The  instances  are  very  numerous,  too 
numerous  to  be  attributed  to  mere  chance,  in  which  the  complaint 
has  first  broken  out  in  those  particular  houses  of  a  town  at  which 
travelers  have  recently  arrived  from  infected  places.  .  .  .  What 
I  wish  to  point  out  now  is  the  fact  that  the  influenza  pervades  large 
tracts  of  country  in  a  manner  much  too  sudden  and  simultaneous  to 
be  consistent  with  the  notion  that  its  prevalence  depends  exclusively 
upon  any  contagious  properties  that  it  may  possess." 

Parkes,  writing  in  Reynolds'  System  of  Medicine  in  1876,  views  the 
subject  more  as  we  see  it  today:  "The  rapidity  of  the  spread  would 
seem  at  once  to  negative  any  connection  between  human  intercourse 
and  the  propagation  of  the  disease;  yet  there  is  some  affirmative 
evidence.  It  does  not  appear  to  follow  the  great  lines  of  commerce; 
but  when  it  has  entered  towns  and  villages  in  which  the  investigation 
can  be  carried  on,  it  is  curious  how  frequently  the  first  cases  have  been 
introduced,  and  how  often  the  townspeople  nearest  the  invalids  have 
been  first  affected.     In  this  country  especially,  Haygarth  in  1775  and 


22  INFLUENZA 

1782,  and  Falconer  in  1802,  collected  so  many  instances  of  this  that 
they  became  convinced  that  its  propagation  was  due  entirely  to 
human  intercourse.  So  also,  when  it  passes  through  a  house,  it 
occasionally  attacks  one  person  after  another.  But  if  it  is  introduced 
in  this  way  it  afterwards  develops  with  marvelous  rapidity,  for  we 
cannot  discredit  the  accounts  of  many  thousands  of  persons  being 
attacked  within  a  day  or  two,  which  is  quite  different  from  the  com- 
paratively slow  spread  of  the  contagious  diseases.  This  sudden 
invasion  of  a  community  makes  it,  to  many  persons,  appear  highly 
improbable  that  any  effluvia  passing  off  from  the  sick  should  thus  so 
rapidly  contaminate  the  atmosphere  of  a  whole  town. 

"Still,  we  must  remember  how  singularly,  of  late  years,  the  knowl- 
edge of  the  introduction  of  cholera  by  persons  coming  from  infected 
districts  has  increased,  and  how  very  striking  are  the  instances  of  this 
kind  already  recorded  in  several  works  on  influenza. 

''In  some  cases,  again,  isolation  or  seclusion  of  a  community,  as 
in  prisons,  has  given  immunity;  or  at  least  that  community  has  not 
been  attacked." 

The  great  rapidity  of  spread  has  caused  even  in  1918  some  tempo- 
rary doubt  as  to  the  contagiousness  of  the  disease.  Thus,  Zinsser 
wrote : 

"The  opinion  of  direct  and  indirect  transmission  from  man  to  man 
is  also  well  supported  by  a  detailed  study  of  the  epidemiology  of 
individual  outbreaks.  In  our  own  experience  with  epidemics  such  as 
those  at  Chaumont,  Baccarat  and  other  places,  the  suddenness  with 
which  the  malady  attacked  large  numbers  of  people  at  almost  one  and 
the  same  time,  caused  me  at  first  to  be  exceedingly  skeptical  of  accept- 
ing transmission  by  contact  as  the  only  means  of  conveyance.  We 
considered  food  and  insect  transmission  as  possibilities,  and  tried 
our  best  to  find  grounds  for  involving  such  agencies.  But  in  every 
case  we  were  forced  to  return  to  the  conclusion  that  direct  and 
indirect  contact  between  men  came  nearest  to  doing  justice  to  all 
observed  facts." 

There  have  been  many  examples  reported  from  personal  experience 
to  show  that  influenza  is  transmitted  from  man  to  man.  Two  objec- 
tions, however,  have  had  to  be  met,  before  this  view  was  generaUy 
accepted.  First,  it  has  been  claimed  by  some  that  the  disease  spread 
more  rapidly  from  an  assumed  focus  than  individuals  could  travel, 
and  second,  that  instances  were  on  record  of  cases  occurring  spontane- 
ously in  isolated  communities.  Yet  a  third  argument  formerly  raised 
against  the  contagious  character  of  the  disease  was  the  claim  that  it 


AN     Kl'IDKMlOLOd'IC    STUDV  23 

broke  out  in  iiuiss  attacks,  that  large  numbers  became  ill  on  the  same 
day  without  the  occurrenco  of  isolated  antecedent  cases.  The  splendid 
work  of  epidemiologists  following  the  1889  epidemic  appears  to  have 
answered  all  of  these  objections.  Many,  such  as  Leichtenstern,  have 
gone  into  great  detail  on  this  subject.  In  fact,  at  that  time  this  was  the 
question  of  greatest  importance.  Today  we  assmne  the  correctness 
of  the  hypothesis,  and  pass  on  to  consideration  of  other  subjects  of 
more  recent  development.  We  will,  therefore,  review  very  hurriedly 
some  of  the  evidence  quoted  to  prove  that  influenza  is  transmitted 
only  from  man  to  man  and  only  by  human  intercourse. 

Isolated  places. — Has  it  ever  been  shown  that  individuals  completely 
isolated  from  communication  with  communities  where  influenza  is 
present  have,  during  an  epidemic,  developed  the  disease?  Leichten- 
stern, after  a  comprehensive  review,  concludes  as  follows:  "We  have 
not  a  single  example  on  record  where  influenza  has  attacked  individuals 
in  completely  isolated  localities,  as  on  mountain  tops  and  mountain 
passes.  Study  of  this  has  been  undertaken  in  Switzerland  by  F. 
Schmid.  The  same  has  been  true  of  ships  at  sea,  as  has  been  shown 
chiefly  from  the  English  Marine  Reports,  There  have  been  reports  of 
influenza  occurring  in  mid-ocean  and  particularly  in  the  earlier  epi- 
demics, but  the  information  has  been  insufficient," 

Parkes  at  even  an  earlier  period  observed:  "I  cannot  but  consider 
that  we  require  better  evidence  of  ships  being  attacked  in  mid-ocean. 
In  some  of  the  quoted  instances  the  ships  had  been  at  a  port  either 
known  to  be  infected  or  in  which  influenza  was  really  present,  although 
it  had  not  become  epidemic.  As  we  are  ignorant  of  the  exact  period 
of  incubation  some  men  may  have  been  infected  before  sailing." 

Critical  investigation  into  stories  of  spontaneous  infection  in 
isolated  localities  such  as  ships  at  sea  and  island  lighthouses  will  quite 
invariably  demonstrate  that  these  popular  reports  have  been  distor- 
tions of  the  actual  facts.  One  or  two  examples  will  suffice,  Abbott 
records  an  example:  "An  impression  having  gained  some  credence 
that  influenza  had  appeared  on  board  the  squadron  of  naval  vessels 
which  sailed  from  Boston  in  December,  1889,  while  on  their  course 
across  the  Atlantic  and  before  their  arrival  in  Europe,  a  letter  was 
addressed  by  the  writer  to  the  Bureau  of  Medicine  and  Surgery  of  the 
United  States  Navy  for  information  upon  this  point,  to  which  a  reply 
was  received,  as  follows: 

"The  'Chicago,'  'Boston,'  'Atlanta'  and  'Yorktown'  left  Boston 
December  7,  1889,  for  Lisbon,  Portugal,  The  first  three  arrived  at 
Lisbon  on  December  21st  without  having  touched  at  any  port  en  rouU-. 


24  INFLUENZA 

The  'Yorktown'  arrived  at  that  port  December  23d,  having,  stopped 
about  twenty-four  hours  at  Fayal,  Azores  .  .  .  Influenza  first 
appeared  on  the  'Chicago'  December  23d,  on  the  'Boston'  Decem- 
ber 28th,  on  the  'Atlanta'  December  30th  and  on  the  'Yorktown' 
December  28th. 

"Influenza  was  prevaiHng  in  Lisbon  at  the  date  of  arrival  of  the 
squadron." 

In  March,  1920,  the  author  was  notified  of  a  somewhat  similar 
story  which  he  undertook  to  trace.  The  results  show  well  the 
inaccuracy  of  verbal  transmission  through  several  individuals.  A 
letter  was  first  sent  to  the  Quarantine  Officer  at  Portland,  Maine: 
"It  has  been  reported  to  us  that  in  a  lighthouse  just  outside  of  Port- 
land, Maine,  there  has  been  a  rather  interesting  prank  played  by 
influenza.  We  are  told  that  three  men  and  one  woman  live  in  the 
lighthouse;  that  during  the  1918  influenza  epidemic  the  woman  con- 
tracted the  disease  while  none  of  the  men  became  sick,  and  that  in  the 
present  epidemic  all  three  of  the  men  became  sick  with  the  disease  and 
the  woman  remained  well.  It  was  claimed  that  they  had  had  no 
communication  with  the  mainland  for  some  time  before  the  men 
became  ill,"  etc. 

The  reply  was  as  follows:  "I  have  inquired  of/the  Light  House 
Inspector's  office  in  Portland  and  they  know  of  no  stations  to  which 
the  terms  of  your  inquiry  would  apply.  ]  > 

"At  the  Boon  Island  station,  there  are  three  keepers  with  families. 
At  the  Half  Way  Rock  station,  there  are  three  keepers  but  no  woman. 
The  Inspector  does  not  seem  to  know  of  any  station  where  there  are 
three  men  and  one  woman." 

A  second  letter,  sent  to  the  Inspector  of  Lighthouses  at  Portland 
brought  corroborative  information: 

"The  Boon  Island  Light  Station  was  stricken  by  this  epidemic  in 
the  following  manner:  The  keeper,  his  wife  and  five  children  were  all 
stricken,  the  keeper  himself  having  had  the  hardest  battle,  having 
apparently  been  subject  to  same  while  ashore  in  Portsmouth,  N.  H. 
after  provisions,  supplies,  etc.  The  2d  assistant's  wife  and  two  chil- 
dren were  also  stricken,  but  the  2d  assistant,  himself,  and  the  1st 
assistant  keeper  did  not  contract  the  malady  in  spite  of  the  fact  that 
they  were  all  confined  on  a  small  island  working  together  at  the  station. 

"During  the  year  1920  none  of  the  keepers  oi-  their  families,  con- 
sisting of  thirteen  in  niimber,  were  affected.  The  Halfway  Rock 
Light  Station  where  three  keepers  are  employed  did  not  contract  this 
malady  either  in  the  years  1918  or  1920. 


AN    KPIDEMIOLOfilC    STIDV  25 

"For  your  inroniuitiou  I  might  tuUl  tluit  during  tho  inspection  trip 
in  tlie  months  of  January,  February  and  March,  1920,  all  of  the  light 
stations  in  this  district  were  visited,  and  it  was  found  that  they  were  all 
enjoying  good  liealth  and  liad  not  been  visited  by  the  epidemic,  with 
the  possible  exception  of  three  stations  which  are  located  either  on  the 
mainland  or  close  to  where  the  keeper  or  his  family  were  able  to  visit 
the  nearby  cities  or  towns." 

Although  it  has  not  been  shown  that  completely  isolated  places 
have  liecn  visited  by  the  disease,  there  is  abundant  evidence  that 
such  places  have  remained  influenza  free  as  long  as  the  isolation  has 
remained  complete.  Islands  and  lighthouses,  which  have  not  been  in 
communication  with  the  mainland,  individuals  living  isolated  on 
mountain  tops,  and  ships  at  sea  remained  free  from  influenza  even  in 
the  presence  of  a  pandemic,  as  long  as  they  did  not  come  into  com- 
munication with  individuals  sick  with  the  disease.  The  following 
places  remained  free  from  influenza  throughout  the  1889  epidemic:  the 
Isle  of  Man,  several  of  the  islands  of  the  West  Indies,  particularly 
the  Bahamas,  Granada  and  St.  Lucia,  also  the  British  Honduras, 
British  Guiana,  and  the  Seychelle  Islands. 

Even  in  1918,  when  the  paths  of  commerce  reached  nearly  every 
portion  of  the  world,  we  have  examples  of  relative  immunity  of  isolated 
places.  Thus  we  know  that  the  Esquimaux  were  attacked  late  in  the 
course  of  the  pandemic,  and  we  have  the  statement  of  Barthelemy  who 
traveled  in  1919  to  some  of  the  oasis  towns  of  the  Sahara  Desert,  and 
there  discovered  that  there  had  not  only  been  no  influenza  up  to  that 
time,  but  also  that  they  had  not  even  heard  of  the  pandemic. 

Another  type  of  isolated  place  is  the  closed  institution.  As  early 
as  1709,  Lancisi  remarked  that  the  prisons  of  the  Inquisition  in  Rome 
remained  free  from  influenza.  Twenty-one  prisons  in  Germany  in 
1889-90  remained  entirely  free  from  the  disease.  This  was  true  of  39 
prisons  in  England,  some  of  which  were  in  cities  where  the  epidemic 
was  most  extensive.  Linroth,  who  observed  this  same  phenomenon  in 
Sweden,  makes  the  wise  remark  that,  "the  influenza  conquers  more 
easily  the  space  of  500  to  1,000  kilometers  than  it  does  the  small  barrier 
made  by  a  prison  wall."  A  convent  in  Charlottenburg  housing  one 
hundred  women  remained  entirely  free  during  the  1889-90  epidemic. 

As  a  rule  institutions  of  this  sort  have  been  unable  to  maintain  a 
complete  quarantine  throughout  the  period  of  an  epidemic,  and  the 
relative  immunit}^  has  been  demonstrated  more  in  late  invasions,  at  a 
time  when  the  restrictions  have  become  somewhat  lax.  Thus,  in  1918, 
Winslow  and  Rogers,  report  that  in  an  orphan  asylum  in  Xew  Haven, 

3 


26  INFLUENZA 

Connecticut,  which  had  completely  escaped  during  the  month  of 
October  when  the  epidemic  was  at  its  height,  one  of  the  Sisters  and 
the  priest  in  charge  came  down  with  influenza  about  December  15th. 
By  the  27th  of  December  127  cases  had  occurred  in  the  institution 
within  twenty-four  hours,  and  by  January  7th  there  had  been  424 
cases,  with  seven  deaths  out  of  a  total  population  of  464.  The  proba- 
ble source  of  the  sudden  outbreak  of  December  27th  seems  to  have  been 
the  Sister  first  affected  who,  when  convalescent,  resumed  her  duties 
in  the  kitchen,  which  included  the  inspection  and  handling  of  the  milk 
given  out  to  the  children. 

Crowd  gatherings. — Yet  another  phenomenon  which  would  lead  us 
to  conclude  that  human  intercourse  is  the  most  potent  factor  in  the 
transmission  of  influenza  is  the  fact  that  there  is  frequently  a  high 
increase  in  the  influenza  rate  following  crowd  gatherings.  Parkes 
observed  long  ago  that  persons  in  overcrowded  habitations,  particu- 
larly in  some  epidemics,  suffered  especially,  and  several  instances  are 
on  record  of  a  large  school  or  a  barracks  being  first  attacked  and  the 
disease  prevailing  there  for  some  days,  before  it  became  prevalent  in 
the  towns  around. 

In  England,  the  weekly  market  played  an  important  role  in  the 
spread  of  the  disease  in  1889.  One  frequently  saw  such  reports  as 
that:  "The  first  case  of  influenza  was  a  man  who  went  to  London 
daily."  Or,  "All  the  earliest  cases  were  men  going  to  London  daily, 
while  their  wives  and  families  were  later  affected." 

In  the  epidemics  at  San  Quentin  Prison,  it  was  noted  that  apices 
of  incidence  usually  occurred  on  Tuesday  and  Wednesday.  During 
the  first  epidemic  it  was  these  days  of  the  second  and  third  weeks. 
Stanley  sees  a  direct  connection  between  this  fact  and  the  fact  that 
every  Sunday  morning  large  groups  of  the  men  were  crowded  together 
in  a  comparatively  small  auditorium  where  they  saw  moving  pictures. 
On  Sunday,  October  20th,  they  sought  to  eliminate  this  source  of 
spread  by  having  a  band  concert  in  the  open  air,  but  the  prisoners 
crowded  around  the  band  and  were  loud  in  their  cheers,  and  on  the 
following  day  there  was  a  large  increase  in  hospital  admissions. 

On  November  24th  after  the  second  epidemic  had  apparently 
ceased  the  picture  shows  were  again  started  after  having  been  closed 
for  over  six  weeks.  The  following  Tuesday  and  Wednesday  twentj''- 
four  weU  defined  new  cases  were  admitted  to  the  hospital.  On 
Thanksgiving  Day  there  was  a  field  meet  between  the  various  depart- 
ments of  the  prison.  About  200  prisoners  took  active  part,  while 
1,600  prisoners  were  spectators.     The  meet  was  held  in  the  open  air, 


AN    EPIDEMIOLOGIC    STUDY  27 

but  the  prisoners  were  closely  packed  and  they  cheered  and  yelled. 
For  the  three  days  following  this  celebration  there  were  9,  5  and  8 
patients  adniittcMl  respectively. 

In  discussing  the  recrudescence  of  influenza  in  Boston  in  November 
and  December,  Woodward  remarks  as  follows : 

"Whether  or  not  it  may  be  more  than  a  succession  of  coincidences 
it  is  certainly  of  interest  to  note  that  the  November  outbreak  of 
influenza  showed  itself  three  days  after  the  Peace  Day  celebration  on 
November  12th,  when  the  streets,  eating  places  and  public  convey- 
ances were  jammed  with  crowds;  that  the  December  epidemic  began 
to  manifest  itself  after  the  Thanksgiving  holiday,  with  its  family 
re-unions  and  visiting;  and  that  reported  cases  mounted  rapidly 
during  the  period  of  Christmas  shopping,  reaching  a  maximum  a  week 
after  the  holiday."  That  this  may  have  been  a  coincidence  is  indi- 
cated bj^  the  fact  that,  according  to  reports  by  Pearl  and  others  this 
was  not  consistently  true  in  other  large  cities. 

Dr.  Meredith  Davies  records  the  case  of  a  hostel  in  Wales  accommo- 
dating 200  students.  Infection  was  introduced  on  October  19th  on 
the  occasion  of  a  dance  attended  by  some  students  from  an  infected 
institution  in  the  neighborhood.  Four  cases  occurred  on  the  20th 
and  within  the  short  space  of  five  days  seventy-nine  students  out  of 
the  200  were  attacked. 

Parsons  found  numerous  similar  examples  in  the  epidemic  of  1889. 
In  1918  it  was  frequently  observed  that  among  American  Soldiers  in 
France,  those  troops  quartered  in  barracks  suffered  a  much  more  rapid 
spread  of  the  disease  than  those  billetted  out  among  the  houses  of  the 
towns. 

Mass  attack. — Another  argument  formerly  raised  against  the 
contagious  character  was  the  claim  that  it  broke  out  in  mass  attack, 
and  large  numbers  became  ill  on  the  same  day  without  the  occurrence 
of  isolated  antecedent  cases.  The  first  cases  of  such  epidemic  diseases 
as  the  plague  and  small  pox  became  a  matter  of  record  because  of  the 
accompanying  high  mortality,  while  in  influenza,  with  its  relatively 
low  death  rate  the  record  usually  begins  only  after  a  comparatively 
large  mass  of  individuals  have  been  attacked. 

Watson  in  1847  observed  as  follows:  "Although  the  general 
descent  of  the  malady  is,  as  I  have  said,  very  sudden  and  diffused, 
scattered  cases  of  it,  like  the  first  droppings  of  a  thunder  shower,  have 
usually  been  remembered  as  having  preceded  it.  The  disorder  is 
most  violent  at  the  commencement  of  the  visitation;  then  its  severity 
abates;  and  the  epidemic  is  mostly  over  in  about  six  weeks.     Yet  the 


28     '  INFLUENZA 

morbific  influence  would  seem  to  have  a  longer  duration.  In  a  given 
place  nearly  all  the  inhabitants  who  are  susceptible  of  the  distemper 
suffer  it  within  that  period,  or  become  proof  against  its  power.  But 
strangers,  who,  after  that  period,  arrive  from  uninfected  places  have 
not,  apparently,  the  same  immunity." 

Parkes  in  1876  observed  that,  "When  the  disease  enters  a  town  it 
has  occasionally  attacked  numbers  of  the  inhabitants  almost  simul- 
taneously. But  more  frequently  its  course  is  somewhat  slower;  it 
attacks  a  few  families  first  and  then  in  a  few  days  rapidly  spreads; 
the  accounts  of  thousands  of  persons  being  at  once  attacked  at  the 
onset  of  the  disease  are  chiefly  taken  from  the  older  records,  in  which 
the  suddenness  of  the  outbreak  is  exaggerated.  Frequently,  perhaps 
always,  in  a  great  city  the  outbreak  is  made  up  by  a  number  of  localized 
attacks,  certain  streets  or  districts  being  more  affected  than  others,  or 
being  for  a  time  solely  affected,  and  in  this  way  it  successively  passes 
to  different  parts  of  the  city.  It  has  generally  occurred  in  a  great  city 
before  appearing  in  the  smaller  towns  and  villages  round  it  and  some- 
times these  towns,  though  in  the  neighborhood,  have  not  been  invaded 
for  some  weeks. 

"In  some  cases  and  perhaps  a  large  number,  it  breaks  out  after 
persons  ill  with  influenza  have  arrived  from  infected  places. 

"The  decline  in  any  great  town  is  less  rapid  than  its  rise,  and 
usually  occupies  from  four  to  six  weeks,  or  sometimes  longer." 

Detailed  studies  of  the  Munich  epidemic  of  1889  and  numerous 
similar  studies  of  the  recent  epidemic,  which  will  be  referred  to  later, 
have  shown  a  period  of  two  or  three  weeks  of  steadily  increasing 
numbers  of  cases  before  the  height  of  the  epidemic  was  reached. 

Droplet  infection  and  spread  through  inanimate  objects. — The  actual 
mode  of  spread  of  the  virus  of  influenza  from  one  individual  to  another 
is  unknown.  The  more  generally  accepted  explanation  is  that  the 
infecting  agent  leaves  the  body  through  the  respiratory  tract,  usuall}^ 
in  the  spray  of  coughing  or  talking;  contagion  is  by  droplet  infection, 
as  is  sometimes  the  case  in  other  respiratory  infections.  Thorne  and 
others  have  called  attention  to  the  capillary  congestion  of  the  con- 
junctivae very  early  in  the  disease.  They  suggest  that  possibly  the 
mucous  membrane  of  the  eye  is  the  site  of  infection. 

There  has  recently  been  considerable  discussion  concerning  the 
spread  of  influenza  through  inanimate  objects. 

Leichtenstern  reviews  the  reports  of  1889-93  in  which  influenza 
was  supposed  to  have  been  transmitted  through  wares,  merchandise 
and  other  inanimate  objects.     He  concluded  that  the  evidence  in  all 


A\    ki'ii)i;mi()L()i;ic  sti'dv  2\) 

of  tlu>  c'jisos  cited  was  insuflicii-iit  lor  conclusive  |)i{)ol".  Siu-li  uii 
example  was  the  supposed  importation  of  the  disease;  in  ^oods  sent 
from  Russia  to  the  (brands  Magazins  (hi  Louvre  at  Paris.  In  one  day 
100  people  became  ill  and  in  a  few  more  500  were  sick  with  influenza. 
The  explanation  was  that  the  germs  had  been  imported  in  goods  sent 
from  Russia  to  the  store.  Detailed  investigation  showed  that  this 
could  not  have  been  the  case  because  no  goods  had  been  received 
from  Russia  for  a  period  of  three  years.  Another  example  is  that  of 
one  of  the  two  winter  caretakers  at  the  St.  (lothard  Hospice.  One  of 
the  two  men  went  down  into  the  valley  where  he  purchased  suppliers. 
Ten  days  after  his  return  the  man  who  had  remained  in  the  Hospice  fell 
ill  with  influenza  while  his  comrade  remained  well.  It  was  stated 
that  influenza  was  introduced  into  Basel  by  goods  shipped  to  that 
place  from  the  Magazins  du  Louvre  in  Paris.  The  first  case  occurred  in 
a  man  who  had  been  working  at  unpacking  these  goods. 

Lynch  and  Gumming  believe  that  droplet  infection  plays  but  a 
minor  role  in  the  spread  of  sputum-borne  diseases,  but  that  insanitary 
methods  of  washing  dishes  and  eating  utensils  was  the  chief  cause  for 
the  high  rates  of  "sputum-borne"  infections  both  in  army  and  civilian 
life  in  1918.  They  found  that  among  31,000  troops  eating  from 
tableware  which  was  cleaned  by  kitchen  police,  the  influenza  rate  was 
51  per  1,000,  while  among  35,000  eating  from  mess  kits  which  each 
individual  washed  himself  the  rate  was  252  per  1,000.  "Eighty-four 
per  cent,  of  the  cases  occurred  among  those  whose  hands  were  con- 
taminated by  washing  their  own  eating  utensils." 

Among  17,236  emploj^ees  of  hotels,  restaurants  and  department 
stores,  who  ate  from  machine  washed  dishes,  there  occurred  349  cases 
of  influenza,  while  among  4,175  who  ate  from  hand  washed  dishes 
there  were  429  cases.  The  rate  was  but  20  per  1,000  in  the  former, 
while  in  the  latter  group  it  reached  103  per  1,000.  Here  again  the 
chances  of  infection  between  the  two  groups  were  as  one  is  to  five. 

These  authors  have  records  covering  252,186  individuals  in  scat- 
tered institutions  in  the  United  States.  Among  those  eating  from 
machine-washed  dishes  the  rate  was  108  per  1,000  while  those  eating 
from  hand-washed  dishes  suffered  at  the  rate  of  324  per  1,000.  The 
ratio  was  1  to  3  between  the  two  groups.  Seventy-five  per  cent,  of 
the  cases  occurred  in  that  group  which  ate  from  dishes  not  disinfected 
with  boiling  water.  They  do  not  state  the  number  of  individuals  in 
each  of  the  two  groups. 

Lynch  and  Gumming  claim  that  in  the  act  of  coughing  only  a  few 
organisms  are  expelled  from  the  mouth,  rarely  over  1,500,  and  con- 


r 


30  INFLUENZA 


elude  that  transmission  by  direct  contact  thiough  the  air  route  but 
rarely,  if  ever,  takes  place.  While  about  1,500  organisms  are  expelled 
onto  the  floor  by  an  act  of  coughing,  a  sterile  glove  wiped  across  the 
lips  may  pick  up  nearly  2,000,000  organisms.  Such  organisms  may 
be  readily  transferred  to  inanimate  objects  which  are  handled  by 
many  people. 

Hemolytic  streptococci  and  pneumococci  may  be  isolated  with 
great  regularity  from  the  hands  of  carriers  or  patients,  from  table 
ware,  inanimate  objects  touched  by  these  patients,  and  from  floor 
dust.  Diphtheria  and  tubercle  bacilli  have  been  isolated  from  the 
hands  and  eating  utensils  of  patients.  The  average  count  of  a  large 
number  of  restaurant  dishwater  specimens  was  4,000,000  bacteria  per 
c.c.  The  temperature  of  this  water  averaged  43°  C.  and  the  dishes 
were  practically  never  scalded.  The  water  was  often  so  highly  pol- 
luted, "that  the  dishes  are  more  highly  contaminated  after  they  are 
washed  than  before  washing  begins.  The  spoon  or  fork  is  often  freer 
from  organisms  just  after  being  used  by  the  restaurant  patron 
than  when  taken  from  the  restaurant's  polluted  dish  water." 

Major  John  S.  Billings,  epidemiologist  at  Camp  Custer,  reported 
that  one  of  the  larger  organizations  did  not  properly  observe  the  regula- 
tion requiring  that  all  mess  kits  and  table  equipment  be  properly 
sterilized.  The  disease  appeared  early  and  spread  unusually  rapidly 
in  this  particular  organization. 

In  summaiizing  the  subject  of  transmission  through  utensils,  we 
may  say  that  the  evidence  is  suggestive  but  inconclusive.  It  is  pos- 
sible, even  probable,  that  this  is  one  mode  of  transmission.  That  it 
is  the  most  important  has  not  been  proved.  Lynch  and  Cumming 
do  not  take  into  consideration  that  the  regiments  with  more  sanitary 
methods  of  cleansing  the  dishes  are  apt  to  be  those  regiments  with 
more  sanitary  habits  throughout  their  daily  routine.  Those  restaurants 
using  mechanical  dish  washers  are  usually  the  cleaner  restaurants. 

Pontano  in  Italy  is  quoted  by  the  Ofl&ce  International  d'Hygiene 
Publique  as  having  obi>erved  in  his  epidemiological  study  that  there  was 
a  constant  connection  between  the  Hving  conditions  and  the  severity  of 
the  complications.  Notable  differences  were  observed  in  neighboring 
houses  according  to  the  hygienic  conditions  of  the  various  households. 

Healthy  carriers  and  convalescents. — ^Leichtenstern,  who  apparently 
accepted  the  Pfeiffer  bacillus  as  the  cause  of  influenza,  did  not  believe 
that  the  disease  could  be  transmitted  by  healthy  carriers.  He  based 
this  assumption  on  the  statement,  made  by  Pfeiffer,  that  the  influenza 
bacillus  was  only  found  in  acute  influenza  cases.     In  the  past  few 


AN    KPIDEMIOLOGIC    STUDY  31 

years  it  has  boon  ulmndantly  shown,  however,  tlial  the  influenza 
bacilhis  can  and  does  exist  on  tlie  mucous  membranes  of  healthy 
indivichials. 

The  outbreak  in  an  orphan  asylum  in  New  Haven  has  been  previ- 
ously described.  There  the  probable  source  of  the  sharp  outbreak 
of  December  27th  seemed  to  be  the  sister  who,  on  corivaUiscence, 
resumed  her  duties  in  the  kitchen.  There  she  inspected  and  handled 
the  milk  served  to  the  children.  This  suggests  the  possibility  of 
infection  being  propagated  by  convalescents  and  by  food. 

At  present  we  do  not  know  whether  or  not  a  patient  remains 
infectious  after  the  acute  symptoms  have  subsided;  we  are  ignorant 
as  to  whether  a  convalescent  patient  can  transmit  the  disease;  and  we 
are  not  certain  whether  the  organism  found  in  healthy  carriers  is 
virulent  or  not.  The  information  at  hand  strongly  indicates  that 
apparently  healthy  individuals  may  transmit  the  infection,  but 
the  wide  distribution  of  the  disease,  with  multiple  possible  sources 
of  infection  for  each  individual,  and  the  relative  insusceptibihty  of 
experimentally  exposed  individuals  has  made  it  impossible  so  far  to 
answer  these  questions  satisfactorily. 

General  Manner  of  Spread  in  iNDrviDUAL  Localities. 

Having  discussed  the  mode  of  propagation  of  influenza  among 
individuals  we  will  follow  the  disease  as  it  attacks  one  person  after 
another  in  a  community  and  study  the  epidemiologic  picture,  drawn 
no  longer  with  the  individual  as  a  unit,  but  with  the  community  as  the 
unit. 

We  must  here  distinguish  between  a  primary  epidemic,  the  first 
wave  of  a  progressing  pandemic,  and  the  secondary  type  in  which  may 
be  grouped  those  large  or  small  recurrences  which  light  up  for  a  period 
of  one  to  three  or  more  j'ears  after  the  primary  wave. 

Primary  type  of  epidemic. — One  of  the  first  important  statistical 
studies  on  this  subject  was  that  of  P.  Friedrich  who  charted  the 
influenza  morbidity  in  Munich  between  the  months  of  December, 
1889,  and  February,  1890.  Similar  observations  have  been  made  by 
Parsons,  Raats,  Linroth,  and  H.  Schmid,  following  the  1889  epidemic. 

Between  the  occurrence  of  the  first  known  case  of  influenza  and  the 
time  of  the  first  very  definite  increase  in  influenza  incidence  in  a 
community,  which  interval  may  be  termed  the  invasion  period,  there  is 
as  a  rule  two  weeks.  During  this  period,  of  course,  more  and  more 
cases  are  occurring,  but  remain  usually  sufficiently  isolated  to  attract 
no  public  notice.     From  this  point  the  epidemic  develops  very  rapidly 


32  INFLUENZA 

and  reaches  its  peak,  usually  within  two  or  at  most  three  weeks.  In 
another  two  or  three  weeks  the  incidence  has  fallen  away  nearly  to 
normal.  The  epidemic  period  comprises  from  four  to  six  weeks,  or, 
including  the  invasion  period,  an  entire  duration  of  six  to  eight  weeks. 
This  is  the  picture  produced  in  a  community  by  a  primary  uncompli- 
cated epidemic  of  influenza.  Greenwood  well  describes  the  salient 
features  of  a  primary  epidemic  as  "first  a  rapid  and  quasi-symmetrical 
evolution,  and  second,  a  frequency  closely  concentrated  around  the 
maximum."  In  other  words  the  duration  is  short,  the  rise  to  a  peak 
rapid,  and  the  subsequent  fall  equally  rapid.  He  showed  that  in  the 
July  and  August,  1918  epidemic  in  Great  Britian  nearly  80  per  cent,  of 
the  total  incidence  in  the  localities  studied  was  grouped  within  three 
weeks  time.  His  curve  corresponds  so  well  with  that  of  the  Munich 
epidemic  that  he  is  able  to  superimpose  them  (Chart  I).  The  rapid 
rise  to  a  peak,  almost  explosive  in  character,  more  characteristic  of 
this  disease  than  of  any  other,  is  to  be  explained  by  the  high  degree 
of  invasiveness  of  the  organism,  by  the  short  period  of  incubation, 
by  the  fact  that  many  of  the  sick  continue  at  their  work,  thus  spreading 
the  disease,  and  by  the  non-immunity  of  large  masses  of  people, 
together  with  the  fact  that  the  transmission  of  a  respiratory  infection 
is  accomplished  much  more  easily  than  is  any  other  type  of  infection. 
The  author  holds  that  the  infrequency  of  immunity  is  a  most 
important  factor  in  the  production  of  this  type  of  outbreak.  The 
mode  of  transmission  of  influenza  is  the  same  as  that  of  other  respira- 
tory diseases.  The  infectivity  is  probably  no  greater  than  that  of 
measles,  although  that  indeed  is  relatively  great.  The  means  of  trans- 
mission are  presumably  the  same  in  each.  Were  we  able  to  develop  an 
"immunity  for  influenza  of  as  high  degree  and  permanence  as  we  possess 
against  measles,  pandemics  of  influenza  would  disappear.  We  wish 
to  emphasize  that  the  primary  type  of  curve  is  a  phenomenon  not 
peculiar  to  influenza,  but  that  under  certain  circumstances  it  may 
be  found  in  other  infectious  diseases,  and  that  it  would  be  found  more 
frequently  in  the  other  diseases  if  the  immunity  developed  against 
them  was  of  as  short  duration  as  it  appears  to  be  against  influenza. 
If,  for  example,  measles  were  to  break  out  in  a  large  group  of  individu- 
als, none  of  whom  had  had  the  disease,  the  type  of  curve  would  be 
the  same.  We  w'ill  produce  evidence  supporting  our  theor}^  under 
another  subject.  Of  course,  other  factors  such  as  short  incubation 
period  and  unusual  opportunities  for  spread  through  mildly  ill  indivi- 
duals play  a  not  unimportant  role. 


CHART  1 


Munich  Coseb  Lend G n jDeoths 


—  I89G 1691 

■■I832 


The  curves  of  incidence  of  influenza  in  Munich,  and  of  deaths  in  London  during 
the  1889  and  subsequent  epidemics.     (Greenwood.) 


AN    EI'IDK.MIOLOGIC    STUDV  'Mi 

Secondary  li/pvof  epidemic. — Tlicrt'  is  a  decided  dilTereiute  between 
the  curve  of  a  primary  wave  as  it  appears  in  the  onward  rush  of  a  new 
pandemics  and  tliat  of  a  secondary  wave  occurring  at  a  greater  or  less 
interval  following  the  primary  spread.  A  secondary  epidemic  affects, 
according  to  Greenwood,  a  relatively  small  proportion  of  the  popula- 
tion, is  slower  in  reaching  its  maxinuim,  and  thereafter  d(H'lines  slowly 
and  irregularly,  more  slowly  than  it  increases.  The  distribution  of 
the  curve  is  less  symmetrical  and  there  is  less  concentration  around  the 
maximum.  A  secondary  epidemic  may  be  characterized  by  a  much 
higher  fatality  than  a  primary  one. 

We  believe  that  the  configuration  of  a  secondary  type  of  wave  is  due 
chiefly  although  not  entirely  to  a  certain  degree  of  residual  immunity 
in  a  large  number  of  individuals  remaining  from  the  first  spread. 
There  is  a  striking  similarity  between  Chart  I  and  Chart  XXVIII, 
the  latter  showing  the  measles  incidence  in  epidemics  among  rural  or 
chiefly  non-immune  troops  in  the  United  States  army.  Chart  XXIX 
shows  a  similar  epidemic  among  urban  or  chiefly  immune  individuals. 
Here  the  curves  correspond  more  to  those  of  a  secondary  type  of 
influenza  epidemic.  Thus  we  see  that,  in  the  absence  of  immunity, 
other  infectious  diseases  may  produce  the  primary  type  of  curve,  and 
that  this  curve  is  not  a  feature  of  influenza  alone. 

A  striking  difference  between  the  tw'o  types  of  waves  of  influenza 
is  the  uniformitj'  and  relative  constancy  of  the  primary  type  as  con- 
trasted to  the  great  variation  in  the  secondary  type.  The  story  of 
the  first  spread  of  influenza  in  one  community  is  usually  similar  to  that 
of  its  spread  in  any  other  community.  Certain  exceptions  will  be 
alluded  to  later.  But  in  the  case  of  recurrent  epidemics  we  may  find 
them  more  severe  or  much  milder;  we  may  find  that  they  attack  a 
large  number  of  individuals  or  a  very  few;  we  may  even  find  an  entire 
absence  of  recurrent  epidemics  in  certain  communities.  The  primary 
curves  are  relatively  uniform;  the  secondary  curves  are  variable. 

Between  1889  and  1894  in  England  there  were  four  epidemics. 
The  first  was  primary,  symmetrical,  and  lasted  between  December 
and  February,  1889-90.  The  second  was  asymmetrical  and  much  more 
fatal  in  the  localities  studied  by  Greenwood.  It  occurred  in  the  spring 
and  summer  of  1891.  There  was  a  third  epidemic  in  the  autumn  and 
winter  of  1891-92  and  a  fourth  occurred  from  November,  1893  to 
January,  1894.  The  third  epidemic,  according  to  Greenwood,  showed 
some  tendency  to  revert  to  the  primary  type  in  respect  to  symmetry, 
w^hile  the  fatahty  rate  partook  of  the  character  of  a  secondary  epidemic. 


34  INFLUENZA 

Creighton  writes:  ''That  which  chiefly  distinguishes  the  influenza 
of  the  end  of  the  nineteenth  century  from  all  other  invasions  of  the 
disease  is  the  revival  of  the  epidemic  in  three  successive  seasons,  the 
first  recurrence  having  been  more  fatal  than  the  original  outbreak, 
and  the  second  recurrence  more  fatal  (in  London  at  least)  than  the  first. 
The  closest  scrutiny  of  the  old  records,  including  the  series  of  weekly 
bills  of  mortality  issued  by  the  parish  clerks  of  London  for  nearly  two 
hundred  years,  discovers  no  such  recurrences  of  influenza  on  the  great 
scale  in  successive  seasons." 

Greenwood,  who  has  studied  this  subject  in  great  detail  in  England, 
discusses  Creighton's  remarks  as  follows:  "He  would  be  a  bold  man 
who  challenged  the  accuracy  of  Creighton  upon  a  point  of  historical 
scholarship,  and  I  have  only  to  suggest  that  there  are  faint  indications 
of  increased  mortality  in  years  following  primary  epidemics  of  influenza 
prior  to  the  nineteenth  century.  Thus  1675  was  a  year  of  primary 
epidemic  influenza,  fully  described  in  Sydenham's  Observationes 
Medicae. 

"The  nature  of  the  succeeding  constitutions  is  not  clear,  but  the 
deaths  'within  the  bills'  for  1676  were  considerably  more  numerous 
than  in  1675,  although  smallpox,  fever  and  'griping  of  the  guts'  were 
noticeably  less  fatal. 

"In  the  English  Responsoria  (1,  54)  the  epidemic  constitution  of 
1679  is  described  as  a  recurrence  of  that  of  1675 — that  is,  as  having  the 
features  of  primary  epidemic  influenza.  In  the  five  following  years 
intermittents  prevailed,  and  in  one  (1684)  the  mortality  much  exceeded 
that  of  1679,  although  the  deaths  from  smallpox  were  fewer.  Again, 
a  hundred  years  later,  in  1782,  there  was  a  famous  summer  epidemic 
of  influenza  in  London  which  gave  rise  to  much  discussion.  The 
London  mortalities  in  1782  and  1783  were,  however,  almost  equal,  when 
the  smallpox  deaths  (which  were  nearly  three  times  as  numerous  in 
1783  as  in  1782)  are  subtracted  from  the  total  mortality  of  each  year. 

"Whether  these  vague  indications  are  sufficient  to  permit  of  our 
thinking  that  the  epidemic  constitution  of  1889-94  was  not  entirely 
unprecedented  is  disputable.  But  the  contrast  of  the  latter  period 
with  the  preceding  single  epidemic  of  1847-48  is  striking;  that  was  a 
primary  epidemic  without  important  sequelae. 

"We  have  now  to  consider  whether  our  experience  this  3^ear  is 
concordant  with  that  of  the  early  nineties,  a  reversion  to  the  earlier 
type,  or  a  new  phenomenon." 

After  comparing  the  1889  curves  with  those  for  the  July,  1918, 
outbreak  in  England,  Greenwood  concludes:  "I  believe  that  the  evi- 


AN     KIMDIOMIOLOCIC    STCDV  35 

dcnco  just  prosotitcd  ('stal)lislies  a  substantial  iilcnlity  between  the 
sunuuer  outbreak  of  191S  and  the  primary  wave  of  1H89-90.  We  do 
not  need  to  ap|)eal  to  any  new  factor  arising;  out,  of  the  war  to  account 
foi-  il. 

"1  next  consider  tlu>  sccon(htry  epidemic  which  we  are  now  experi- 
encing (October,  1918).  Evidently  our  knowledg(>  of  the  events  in 
1891  wouUl  lead  us  to  feel  no  surprise  at  the  emergence  of  a  secondary 
wave,  although  we  could  not  be  sure  tiiat  the  precedent  of  1S17 
would  not  be  followed. 

"The  summer  epidemic  of  1918  in  the  Royal  Air  Force  included 
nearly  80  per  cent,  of  the  total  incidence  within  the  three  weeks  con- 
taining the  maxinmm,  and  the  Munich  epidemic  included  just  over  80 
per  cent,  within  the  same  limits.  Now  if  the  current  epidemic  has 
reached  its  maximum,  not  more  than  65  per  cent,  of  the  incidence  will 
probably  be  so  concentrated,  and  the  duration  will  therefore  be  longer 
than  in  the  summer;  if,  as  suggested  by  the  ratio  of  the  last  two  ordi- 
nates,  the  maximum  is  not  yet  attained,  then  the  quota  of  the  three 
first  weeks  is  likely  to  be  still  smaller  and  the  complete  duration  still 
longer. 

"The  diagram  of  factory  sickness  leads  to  the  same  inference,  which 
is  that,  from  the  standpoint  of  prevalence,  the  present  is  a  typical 
secondary  epidemic,  congruent  with  that  of  1891. 

"It  appears,  then,  that  the  origin  of  the  summer  epidemic  nuist  be 
explained  upon  such  epidemiological  principles  as  will  account  for  the 
primary  wave  of  1889-90,  that  the  current  outbreak  is  in  pari  materia 
with  that  of  1891,  its  excessive  mortality  being  mainly  due  to  the 
accident  of  season,  aided  by  the  special  circumstances  of  overcrowding 
and  fuel  shortage  which  are  due  to  the  war.  In  a  word,  this  is  not 
essentially  a  war  epidemic." 

Wutzdorff  found  that  in  some  towns,  particularly  in  North  Ger- 
many, the  1891-1892  wave  was  almost  as  extensive  as  that  of  1889-90 
had  been  in  other  places,  but  that  in  general  the  morbidity  in  Germany 
was  much  lower.  He  bases  these  conclusions  on  a  studj^  of  the  extent 
of  crowding  in  the  hospitals  in  the  two  years,  on  statistics  of  govern- 
ment physicians,  etc. 

In  Europe  the  recurrent  epidemics  of  1891  increased  as  a  rule  very 
gradually,  developed  slowly,  reached  their  high  point  frequently 
after  many  weeks,  and  as  gradually  decreased.  The  epidemic  duration 
in  the  winter  of  1891-92  lasted  four  or  five  months.  The  morbidity 
in  spite  of  the  longer  duration  was  decidedly  less.  This  is  very  differ- 
ent from  the  explosive  appearance  of  1889  when  the  peak  was  reached 


36  INFLUENZA 

in  fourteen  days  and  the  whole  epidemic  had  been  completed  in  six  to 
eight  weeks.  There  were  some  exceptions  to  this  rule,  as  in  Yorkshire, 
England,  where  the  epidemic  broke  out  suddenly  between  the  11th 
and  13th  of  April,  1891,  had  reached  its  peak  after  ten  days,  and  for 
another  twenty  days  declined.  Especially  interesting  was  Sheffield, 
where  the  first  spread  began  gradually  and  ran  a  slow  course,  while  the 
second  epidemic  of  1891  began  explosively,  lasted  a  short  time  and 
decHned  rapidly,  but  showed  a  significantly  greater  mortality  than 
that  of  1889. 

The  experiences  in  various  communities  in  the  United  States  have 
been  not  unlike  those  described  for  European  cities.  Abbott  in 
describing  the  successive  epidemics  in  Massachusetts  remarked  that 
the  1889-90  spread'  manifested  itself  by  a  sudden  rise  in  the  mortality 
from  influenza  and  pneumonia,  beginning  about  December  20th  and 
culminating  in  the  middle  week  of  January,  thereafter  falKng  off  quite 
suddenly  in  February  to  about  the  usual  rate  for  these  diseases.  The 
second  epidemic  two  years  later  began  with  a  more  gradual  rise  in 
October  and  November  and  then  increased  sharply  in  December, 
continued  for  nearly  three  weeks  at  its  maximum  in  January,  and 
dechned  nearly  as  sharply  as  in  the  previous  epidemic  two  years 
before. 

Winslow  and  Rogers  who  have  studied  the  1918  epidemic  as  it 
affected  the  various  towns  of  Connecticut  observed  that  the  outbreak 
in  a  given  community  generally  occupied  a  period  of  from  six  to  eight 
weeks,  and  was  steep  and  abrupt  in  communities  which  were  badly 
hit,  flatter  and  more  gently  sloping  in  those  which  escaped  lightly. 
Also  the  outbreak  was  more  severe  in  communities  receiving  the 
infection  early  than  in  those  later  affected. 

Mortality  curves. — Pearl  has  studied  the  epidemic  constitution  of 
influenza  in  forty-two  of  the  large  cities  of  the  United  States.  He  has 
plotted  the  annual  death  rate  per  1,000  population  from  all  causes  in 
each  week,  from  the  week  ended  July  6,  1918,  up  to  January  1,  1919, 
and  observed  a  very  distinct  difference  in  the  type  of  curve  for  deaths 
from  all  causes  during  the  epidemic  period  in  the  various  cities.  These 
differences  have  been  chiefly  in  respect  to  the  severity  and  suddenness 
with  which  they  were  attacked.  Thus  Albany,  Boston,  Baltimore, 
Dayton  and  Philadelphia  show  an  initial  explosive  outbreak  of  great 
force,  while  Atlanta,  Indianapolis,  Grand  Rapids,  Milwaukee  and 
Minneapolis  exhibit  a  much  slower  and  milder  increase  of  the  mortality 
rate.  In  Albany  and  Baltimore  the  curve  of  the  first  epidemic  out- 
break rises  to  a  peak  and  declines  at  about  the  same  rate.     In  Cleve- 


AN    EPIDEMIOLOGIC    STUDY  37 

land  and  St.  Paul,  on  the  other  hand,  the  rate  of  ascent  to  the  peak 
is  very  rapid,  while  the  decline  is  slow  and  long  drawn  out. 

Some  of  the  cities,  such  as  Albany,  show  hut  a  single  well  dcfhicd 
peak  in  the  mortality  curve.  Others,  such  as  Boston,  New  Orleans 
and  San  Francisco  show  two  peaks;  while  still  others,  like  Louisville, 
show  three  well  marked  peaks. 

Usually  the  first  was  the  highest  and  the  second  and  third  were 
progressively  lower.  Milwaukee  and  St.  Louis,  on  the  other  hand, 
showed  second  peaks  higher  than  the  first.  The  usual  phenomenon, 
however,  was  a  large  first  wave  followed  by  smaller  ones. 

The  highest,  or  maximum  peak-rate  of  mortality  during  the 
epidemic  varied  greatly,  from  3L6  per  1,000  in  the  case  of  Grand 
Rapids,  to  158.3  per  1,000  in  the  case  of  Philadelphia. 

The  death  rates  which  were  of  the  most  frequent  occurrence  were, 
generally  speaking,  rates  below  70  per  1,000  per  week. 

The  date  of  the  week  in  which  the  maximum  peak  rate  occurred  was 
earliest  in  Boston  and  Cambridge,  where  it  occurred  October  5th, 
and  latest  in  Grand  Rapids,  Milwaukee  and  St.  Louis  (December 
14th).  Thirty-one  of  the  40  cities  studied  had  attained  the  peak  rate 
of  mortality  prior  to  November  2d.  In  the  case  of  Milwaukee  and 
St.  Louis  the  maximum  peak  was  the  second  peak,  whereas  in 
Grand  Rapids  it  was  the  first  peak  that  was  so  late.  Sixty-five 
per  cent,  of  the  40  cities  showed  two  distinct  peaks  in  the  mortality 
curve,  while  15  per  cent,  had  one  peak,  and  8  or  20  per  cent,  had  three 
peaks. 

"It  appears  clearl}'-  that  there  was  a  definite  tendency  for  the  two- 
peak  cities  to  fall  into  two  groups  in  respect  of  the  time  elapsing 
between  first  and  second  peaks.  About  a  third  of  them  had  the  second 
mortality  peak  around  eight  weeks  after  the  first  peak.  The  remain- 
ing two-thirds  had  the  second  peak,  on  the  average,  about  thirteen 
weeks  after  the  first.  The  three-peak  curves  had  the  second  peak  on 
an  average  7.1+0.3  weeks  after  the  first,  and  the  third  peak  on  an 
average  13.1  ±0.3  weeks  after  the  second.  The  cycle  in  the  epidemic 
waves  would  therefore  appear  to  be  nearly  a  multiple  of  seven  weeks 
rather  than  the  ten  weeks  tentatively  deduced  from  the  dates  of  peaks. 
There  the  process  of  averaging  obscured  the  true  relations." 

Duration  of  explosive  outbreak. — The  range  of  the  duration  of  the 
first  outbreak  of  epidemic  mortality  is  great,  varying  from  five  weeks 
in  Richmond,  Virginia,  to  twenty-three  weeks  in  Atlanta,  Georgia. 
Twenty  of  the  cities,  one  half  the  total  number,  showed  a  duration  of 
ten  weeks  or  less,  while  in  the  other  half  the  duration  was  eleven  weeks 


38  INFLUENZA 

or  more.  The  mean  duration  of  epidemic  mortality  in  the  first  the  out- 
break was  11.90  +  0.55  weeks.  The  ascending  hmb  of  mortality  rate 
was  rapid  in  nearly  all  cities.  The  descending  limb  was  usually 
slower.  In  34  of  the  40  cities  it  required  four  weeks  or  less  time  for  the 
mortality  rate  to  pass  from  normal  to  its  epidemic  peak.  But  in  only 
half  as  many  (17)  of  the  cities  did  the  rate  come  down  from  its  peak  to 
normal  again  in  a  period  of  four  weeks  or  less.  The  mean  time  from 
normal  mortality  rate  to  peak  was  3.90  +  0.21  weeks.  The  mean  time 
from  peak  mortality  rate  to  normal  was  8.00  ±  0.50  weeks.  Thus  it 
took  about  twice  as  many  weeks  for  the  mortality  curve  to  come  back 
from  its  peak  to  normal,  as  were  required  for  the  increase  from  normal 
to  peak  at  the  beginning  of  the  explosion.  This  is  on  the  average. 
The  ascending  limb  occupied  about  a  month  and  the  descending  limb 
two  months. 

Pearl's  curves  which  have  been  copied  in  this  report  (Charts  II  to 
VII)  enable  us  to  follow  his  conclusions.  Pearl  offers  a  partial  explana- 
tion for  the  variations  in  the  different  cities.  There  can  be  no  doubt 
but  what  many  factors  play  a  role  in  the  causation  of  these  variations, 
and  it  is  to  be  regretted  that  up  to  the  present  no  statistics  for  smaller, 
more  homogeneous  communities  have  as  yet  been  reported  which 
could  be  compared  with  Pearl's  excellent  work  on  the  large  cities  of 
the  country.  Were  his  work  supplemented  by  records  from  smaller 
towns  in  which  the  varying  factors  are  less  numerous,  in  which  there  is 
less  occupational  variation,  additional  conclusions  could  probably  be 
reached.  The  unfortunate  feature  is  that  as  a  rule  statistics  from  the 
smaller  cities  and  towns  are  less  reliable. 

From  a  detailed  mathematical  study  of  influenza  in  39  of  our  largest 
cities,  done  chiefly  by  the  means  of  multiple  correlation,  with  the  hope 
of  being  able  to  explain  the  differences  in  the  epidemic  curves  of  weekly 
mortality  in  the  various  cities.  Pearl  concludes  as  follows: 

"The  general  conclusion  to  which  we  come  from  an  examination  of 
the  correlation  data  assembled  to  this  point  is  that  these  four  general 
demographic  factors,  density  of  population,  geographical  position,  age 
distribution  of  population,  and  rate  of  recent  growth  in  population,  have 
practically  nothing  to  do,  either  severally  or  collectively,  with  bringing 
about  those  differences  between  the  several  cities  in  respect  to  explo- 
siveness  of  the  outbreak  of  epidemic  mortality  in  which  we  are  inter- 
ested. Significantly  causal  or  differentiating  factors  must  be  sought 
elsewhere." 

Concerning  geographical  position,  he  did  find  some  slight  relation- 


("HART   11. 


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CHART  III. 


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CHART  V. 


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Death  rates  from  all  causes  by  weeks  in  certain  large  cities  of  the  United  States 

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CHART  VI 1. 


I 

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Death  rates  from  all  causes  by  weeks  in  certain  large  cities  of  the  United  States 
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AN    EPIDEMIOLOGIC    STUDY  39 

ship  with  linear  distance  from  the  city  of  Boston,  where  the  epidemic 
was  supposed  first  to  have  begun  in  this  country: 

'"This  result  means  that  the  j^rcatci-  the  linear  distance  of  a  city 
from  Boston  the  less  explosive  did  the  outbreak  of  epidemic  mortahty 
in  that  city  tend  to  be.  This  is  in  accord  with  the  goncrul  cpidoniiolo- 
gical  rule  that  the  force  of  an  epidemic  tends  to  diminish  us  it  spreads 
from  its  primary  or  initial  focus.  It  must  be  noted,  however,  that 
the  correlation  coefficient  in  this  case  is  not  large.  It  is  barely  past 
the  value  where  it  may  safely  be  regarded  as  statistically  significant. 
This  fact  may  probably  be  taken  to  mean  that  influenza  does  not  follow 
the  epidemiological  law  referred  to  with  anything  like  such  precision 
as  do  some  other  epidemic  diseases,  notably  poliomyelitis." 

These  factors  having  been  found  to  be  of  little  value  in  his  attempt 
to  explain  the  varying  curves  in  the  39  different  cities,  Pearl  next 
correlated  the  explosiveness  of  the  epidemic  mortality  with  deaths  from 
all  causes,  deaths  from  pulmonary  tuberculosis,  from  organic  heart 
disease,  from  acute  nephritis  and  Bright's  disease,  from  influenza,  from 
pneumonia  (all  forms),  from  typhoid  fever,  from  cancer  and  from 
measles,  in  the  various  cities. 

"The  outstanding  fact  which  strikes  one  at  once  from  this  table  is 
the  high  order  of  the  correlation  which  exists  between  the  explosiveness 
of  the  outbreak  of  epidemic  mortality  in  these  communities  and  the 
normal  death  rate  from  certain  causes  of  death  in  the  same  communi- 
ties. In  the  first  four  lines  of  the  table  the  correlation  coefficients 
range  from  about  6  to  more  than  10  times  the  probable  errors.  There 
can  be  no  question  as  to  the  statistical  significance  of  coefficients  of 
such  magnitude. 

"The  highest  correlation  coefiicient  of  all  is  that  on  the  first  line 
of  the  table,  for  the  correlation  of  epidemicity  index  with  death  rate 
from  all  causes.  The  existance  of  this  high  correlation  at  once  indi- 
cates that  an  essential  factor  in  determining  the  degree  of  explosive- 
ness of  the  outbreak  of  epidemic  influenza  in  a  particular  city  was  the 
normal  mortality  conditions  prevaihng  in  that  city.  In  the  group  of 
communities  here  dealt  with,  those  cities  which  had  a  relatively  high 
normal  death  rate  had  also  a  relatively  severe  and  explosive  mortality 
from  the  influenza  epidemic.  Similarly,  cities  which  normally  have  a 
low  death  rate  had  a  relatively  low,  and  not  sharply  explosive,  increase 
in  mortality  during  the  epidemic. 

"It  will  also  be  noted  that  the  correlation  in  the  next  three  lines 
of  the  table,  namely  those  of  pulmonary  tuberculosis,  so-called,  organic 
diseases  of  the  heart,  and  chronic  nephritis  and  Bright's  disease,  are 


40  INFLUENZA 

of  the  same  order  of  magnitude  as  that  between  the  death  rate  from 
all  causes  and  the  explosiveness  of  the  epidemic  outbreak  of  influenza." 

Pearl  suggests  that  this  correlation  might  arise  because  of  differ- 
ences in  the  constitution  of  populations  in  the  different  cities,  or, 
that  it  was  a  factor  of  geographical  position,  such  as  the  distance  from 
the  Atlantic  seaboard;  but  that  even  after  correction  of  the  results  for 
age  distribution  and  geographical  position,  the  net  correlations  were 
actually  higher  than  were  the  gross  uncorrected  correlations. 

''We  may  conclude  that  the  most  significant  factor  yet  discovered 
in  causing  the  observed  wide  variation  amongst  these  39  American 
cities  in  respect  of  the  explosiveness  of  the  outbreak  of  epidemic  in- 
fluenza mortality  in  the  autumn  of  1918  was  the  relative  normal 
liability  of  the  inhabitants  of  the  several  cities  to  die  of  one  or  another 
of  the  three  great  causes  of  death  which  primarily  result  from  a  func- 
tional breakdown  of  one  of  the  three  fundamental  organ  systems  of 
the  animal  body,  the  lungs,  the  heart  and  the  kidneys." 

Winslow  and  Rogers  studied  the  relation  of  the  pneumonia  death 
rate  from  1901  to  1916  to  the  influenza  death  rate  of  1918  in  40  large 
cities  of  the  United  States  and  found  a  distinct  correlation.  The 
cities  which  have  been  characterized  by  a  high  pneumonia  rate  in  the 
past  are  precisely  the  cities  which  suffered  most  severaly  in  the  1918 
outbreak.  This  is  not  due  especially  to  virulent  types  of  pneumonia 
organisms  in  certain  sections  of  the  country  because  they  found  this 
same  high  correlation  between  total  death  rates  and  influenza  death 
rates,  in  the  same  cities. 

They  believe  that  these  high  correlations  may  be  the  result  of 
weaknesses  in  the  population  due  to  high  incidences  of  organic  diseases 
and  tuberculosis  in  earlier  years,  or  more  probably  that  the  correlation 
is  an  indirect  one,  due  to  the  relation  between  each  of  the  factors 
studied  and  one  or  more  underlying  conditions  affecting  both,  such  as 
age  distribution  of  the  population,  race  distribution,  or  social  and 
economic  conditions  in  the  various  cities  studied.  Or,  finally,  it 
may  be  that  the  high  rate  from  tuberculosis  and  organic  disease  in 
1916  was  due  to  these  latter  factors,  while  the  high  incidence  of  influ- 
enza was  due  chiefly  to  proximity  to  the  original  focus  of  infection. 
None  of  these  explanations  are  considered  entirely  satisfactory. 

It  is  important  to  call  attention  to  the  fact  that  the  American 
observers  quoted  have  been  studying  the  death  rate  from  influenza 
as  it  is  revealed  in  the  increase  of  death  rate  from  all  causes,  whereas 
Leichtenstern  and  Wutzdorff,  and  Greenwood,  in  his  studies  in  the 
Royal  Air  Force  have  concerned  themselves  with  morbidity.     The 


AN    EPlDEMIOLOc;iC    STUDY  41 

comparison  of  morbidity  and  mortality  cannot  be  easily  made  as  we 
will  show  when  discussing  these  two  subjects,  so  we  cannot  conclude 
that  the  work  of  Pearl  and  of  Winslow  and  Rogers  is  at  variance  with 
the  other  work  quoted.  The  mortality  curves  form  another  character- 
istic of  the  local  spread  of  influenza  in  a  community. 

It  is  characteristic  of  influenza  that  the  curve  of  deaths  does  not 
fall  as  rapidly  as  does  the  curve  for  influenza  cases.  Thus  in  morbidity 
curves  we  may  expect  to  find  a  symmetrical  curve  for  a  primary 
epidemic,  but  the  mortality  is  rarely  if  ever  symmetrical,  the  curve 
rising  rapidly  and  falling  very  much  more  slowly. 

Morbidity  curves  in  1920  recurrences. — The  curves  of  influenza 
incidence  in  the  recurrence  of  1920  have  varied  in  different  localities, 
but  in  certain  communities  where  the  record  has  been  carefully 
reported  the  epidemic  appears  to  be  characterized  by  a  symmetrical 
evolution  and  usually  a  lower  death  rate  as  compared  with  1918. 
The  curve  of  incidence  in  the  State  of  Massachusetts  in  January, 
February  and  March,  1920,  is  sjTnmetrical,  if  anything  falhng  away 
more  rapidly  than  it  ascends,  and  the  duration  is  at  least  ten  weeks. 
The  crest  of  the  influenza  wave  in  Massachusetts  was  reached  on 
February  4th,  5th  and  6th.  The  peak  is  recorded  as  being  in  the  week 
of  February  7th. 

During  the  1920  epidemic  the  author  made  a  house  to  house  canvass 
in  six  representative  districts  in  the  city  of  Boston  covering  a  popula- 
tion of  10,000  individuals.  The  curve  of  incidence  of  influenza  cor- 
responds closely  wdth  the  curves  for  the  city  and  the  state  as  a  whole. 
The  peak  was  reached  in  the  same  week,  the  week  ending  February 
7th,  the  curve  was  symmetrical,  and  the  duration  of  the  entire  epidemic 
w-as  about  the  same.  The  morbidity  rate  for  1920,  according  to  our 
influenza  census,  was  but  half  of  that  for  1918  for  the  same  population. 
The  recurrent  epidemic  as  we  will  show  later  was  decidedly  milder 
(see  Chart  XVIII). 

In  Detroit  the  1920  epidemic  reached  its  peak  for  morbidity  on  the 
9th  day,  and  that  for  mortality  on  the  16th.  In  1918  the  morbidity 
peak  was  not  attained  until  the  15th  day  and  the  death  peak  on  the 
22d.  The  recurrent  outbreak  had  nearly  run  its  course  within  three 
weeks.  The  following  comparison  between  the  influenza  incidence  in 
1918  and  1920  in  Detroit  is  taken  from  a  report  by  H.  F.  Vaughan, 
Commissioner  of  Health  for  that  city.  In  it  is  shown  a  comparison 
of  the  total  figures  on  the  twenty-seventh  day  of  each  of  the  two 
epidemics : 


42 


INFLUENZA 


A  Co7nparison  of  the  1918  and  1920  Epidemics  of  Influenza  in  Detroit.     Statistics 
Made  to  Include  Through  the  Twenty-seventh  Day  of  Each  Epidemic. 


1 

influenza 

cases 

Deaths  from 
influenza  and 
pneumonia 

Normal  in- 
fluenza and 
pneumonia 
deaths  for  this 
season 

Excess  in- 
fluenza and 
pneumonia 
deaths  above 
normal 

1920  (Jan.-Feb.) 

1918  (Oct.-Nov.) 

11,202              1,642 
16,423              1,286 

197 
124 

1,445 
1,162 

There  had  been  fewer  cases  reported  on  the  twenty-seventh  day  of 
the  1920  epidemic,  but  these  had  resulted  in  a  greater  number  of 
deaths.  On  this  day  the  recurrent  epidemic  had  run  its  course,  while 
the  1918  one  was  still  in  full  swing.  On  the  twenty-seventh  day  of 
1918  there  were  137  influenza  cases  reported  and  49  deaths.  On  this 
day  in  1920  there  were  but  24  cases  and  34  deaths.  Thus  the  second 
outbreak  was  of  shorter  duration,  but  was  more  deadly  while  it  lasted. 

Seven  weeks  of  the  1920  epidemic  in  Detroit  killed  0.20  per  cent, 
of  the  population,  two  out  of  every  one  thousand  people.  A  similar 
period  at  the  beginning  of  the  epidemic  of  1918  witnessed  the  death 
of  0.17  per  cent,  of  the  population.  This  was  a  smaller  number,  but 
the  epidemic  at  this  time  had  not  completed  its  course,  and  continued 
to  be  more  or  less  prevalent  for  twenty-one  weeks,  resulting  finally 
in  the  death  of  0.28  per  cent,  of  the  population.  The  recurrent  epi- 
demic was  more  highly  fatal,  but,  being  of  shorter  duration,  Detroit 
actually  suffered  less  from  it. 

Spread  in  Countries  and  Continents. 

The  spread  of  influenza  is  usually  not  limited  to  a  single  community. 
Almost  invariably  it  will  travel  on  to  another  locality,  carried  thither 
by  human  intercourse,  and  will  there  build  again  a  local  epidemiologic 
picture  more  or  less  modified  by  changes  in  the  environment  and 
changes  in  the  virulence  of  the  virus  itself. 

Spread  in  primary  waves. — Reference  to  the  table  of  epidemics  in 
history  will  show  that  in  many  of  the  epidemics  and  in  most  of  the 
widespread  epidemics  and  pandemics  there  appears  to  have  been  a 
definite,  clearcut,  direction  of  spread  from  one  locality  to  others.  In 
the  recent  literature  there  has  appeared  considerable  discussion 
concerning  the  site  of  origin,  the  endemic  focus  of  pandemic  influenza. 
Briefly  the  question  raised  is  as  to  whether  there  are  single  or  multiple 
foci.  We  will  for  the  time  ignore  this  perplexing  question.  In  either 
case,  after  the  influenza  virus  has  once  attained  such  communicability 


A\    KPIDKMIOLOOIC    STUDY  43 

as  to  produce  ;i  pandemic  it  does  follow  a  direct  course  over  countries 
and  continents.     Thi.s  may  be  followed  in  resume  in  our  table. 

The  disease  does  not  at  any  time  spread  more  rapidly  than  the 
available  speed  of  human  communication  between  the  areas  affected. 
If  influenza  does  appear  simultaneously  in  two  widely  separated 
communities  without  having  been  brought  there  from  a  common  source 
it  must  be  that  it  arose  spontaneously  from  simultaneous  increase  in 
virulence  of  the  virus  in  those  localities. 

Influenza  was  prevalent  in  Turkestan,  Western  Asia,  in  May  of 
1889.  It  spread  first  to  Tomsk  in  Siberia  and  did  not  appear  in 
Petrograd  until  the  end  of  October.  By  the  middle  of  November  it 
had  reached  Berlin  and  Paris,  and  one  month  later  it  was  epidemic  in 
New  York  and  Boston.  Four  months  had  been  required  for  the 
disease  to  reach  Petrograd  from  Bokhara  in  Turkestan,  while  within 
two  months  thereafter  it  had  traveled  from  Russia  to  the  United  States. 
In  both  cases  the  rapidity  of  spread  corresponded  to  the  rapidity  of 
the  means  of  communication  of  the  locality;  the  caravan  in  Turkestan 
and  the  transatlantic  liner  to  America.  North  America  was  widely 
infected  in  January  of  1890.  So,  also,  Honolulu,  Mexico,  Hong  Kong, 
Japan.  Ceylon  first  experienced  the  epidemic  early  in  February, 
India  at  the  end  of  the  month,  Borneo  and  Australia  on  the  first  of 
March,  Mandalay  towards  the  first  of  May,  China  and  Iceland  in 
July,  Central  Africa  in  August  and  Abyssinia  in  November  of  1890. 

It  should  be  noted  that  influenza  was  reported  to  have  been  preva- 
lent in  Greenland  at  about  the  same  time  that  it  was  in  Bokhara. 
There  appears  to  have  been  no  relationship  between  these  two  out- 
breaks. 

The  spread  of  the  pandemic  may  be  followed  also  by  recording  the 
period  of  greatest  mortality  in  the  various  cities.  This  period  at 
Stockholm  followed  that  at  Petrograd  by  three  weeks,  and  that  of 
Berlin  by  another  w^eek.  The  period  for  Paris  was  a  week  later  than 
for  Berlin,  that  for  London  another  week  later,  and  that  for  Dublin 
three  weeks  later  than  that  for  London.  The  week  of  highest  mor- 
tality in  Dublin  was  later  than  that  for  New  York  or  Boston. 

The  earlier  epidemics  progressed  more  slowly.  That  of  1762  pre- 
vailed in  Germany  in  February,  in  London  in  April,  in  France  in  July, 
and  in  America  in  October.  In  1782  it  attacked  London  in  May, 
Exeter  two  weeks  later  and  Edinburgh  early  in  June.  In  1830-1832 
the  spread  from  ^Moscow  and  Petrograd  through  Germany  required  no 
less  than  eight  months  to  cover  the  latter  countrj-. 

In  1872  the  time  required  for  spread  from  Leipzig  to  Amsterdam 


44  INFLUENZA 

was  eighteen  days,  the  same  time  that  was  required  for  a  merchant  in 
the  latter  town  to  reach  Leipzig. 

There  are  many  instances  on  record  in  which  influenza  has  passed 
by  small  towns  in  its  onward  course  to  attack  a  larger  city  and  only 
at  some  later  date  has  the  small  town,  not  on  the  main  line  of  com- 
munication, been  affected.  Not  only  is  the  speed  of  transportation 
between  two  communities  of  importance,  but  also  the  volume  of  the 
transportation  undoubtedly  plays  a  part  in  the  rapidity  of  develop- 
ment in  a  second  locality.  When  the  disease  is  carried  by  a  vessel  the 
first  places  to  be  attacked  are  the  seaports  and  the  coast  towns,  be  the 
land  a  continent  or  an  island.  From  there  it  spreads  inland  either 
rapidly  or  slowly  according  to  the  transportation  facilities.  Formerly 
the  question  was  raised  whether  influenza  spread  in  continuous  lines 
or  radiated  in  circles.  Naturally  it  follows  the  direct  lines  of  com- 
munication, most  of  which  are  radially  distributed  around  large 
centers. 

Leichtenstern  calls  attention  to  the  fact  that  in  the  1898  epidemic, 
as  in  the  previous  one,  the  general  direction  of  spread  was  from  East  to 
West  across  Europe.  This  was  also  true  of  the  epidemics  of  1729, 
1732,  1742,  1781,  1788,  1799,  1833,  and  1889. 

There  have  been  in  Europe  two  general  routes  followed  by  pande- 
mics, a  Northern  one  through  Russia  and  following  the  lines  of  travel 
into  Germany  and  through  the  countries  of  Europe;  and  a  Southern 
path  coming  from  Asia,  through  Constantinople,  and  entering  Europe 
from  the  South,  particularly  Italy.  With  the  latter,  after  reaching 
Europe,  the  spread  is  northerly;  with  the  former  it  is  southerly,  and 
usually  Spain  was  the  country  last  infected. 

In  the  United  States  as  well,  pandemic  influenza  usually  has  spread 
from  East  to  West,  entering  the  country  at  or  near  New  York  or 
Boston,  and  spreading  West  and  South.  This  was  true  in  the  autumn 
epidemic  of  1918. 

Spread  in  recurrences. — As  a  rule  the  manner  of  spread  of  a  second- 
ary epidemic  following  the  primary  pandemic  wave  is  quite  different. 
At  a  longer  or  shorter  interval  following  the  first  spread  the  disease 
breaks  out  anew  in  one  locality  or  another,  sometimes  simultaneously 
in  widely  separated  districts.  Sometimes  we  can  distinguish  a  direc- 
tion of  spread  in  the  relatively  small  community  affected,  it  frequently 
being  observed  that  the  disease  will  start  up  in  a  large  city  which  has 
experienced  the  illness  during  the  first  pandemic,  and  from  there  will 
spread  to  small  nearby  localities  which  may  have  remained  free  until 
that  time.     Again,  any  clear-cut  direction  of  spread  may  be  entirely 


AN    EPIDEMIOLOGIC    STUDY  45 

lacking;.  It  is  rare  iiidocd  that  an  epidemic  following  another  by  a 
short  interval  will  follow  a  definite  line  over  an  entire  country  or 
continent.  Such  an  example  is,  however,  to  be  found  in  the  epidemic 
of  1833,  which  traveled  over  Europe  from  Russia,  spreading  to  the 
west  and  the  south  and  following  practically  the  identical  path  that 
it  had  taken  in  1830.  Even  so  it  was  not  as  widespread,  for  while  the 
epidemic  of  1830  had  covered  the  entire  earth,  America  appears  to 
have  escaped  the  second  epidemic. 

These  disseminated  and  independent  outbreaks  are  believed  to  arise 
from  endemic  foci  in  which  the  virus  has  been  deposited  during  the 
progress  of  its  first  spread  and  in  which  the  germ  has  survived  until 
it  has  acquired  once  again  exalted  virulence. 

Usually  these  endemic  outbreaks  show  in  their  local  configuration,  a 
secondary  type  of  wave.  That  this  is  not  always  the  case  we  have 
already  indicated.  The  epidemic  of  1732-1733  was  a  recurrence  of 
that  of  1729-1730.  The  epidemic  of  1782  had  as  its  source  the  epi- 
demic of  the  years  1780-1781.  The  epidemic  of  1788  recurred  until 
1800,  and  was  quite  possibly  associated  with  those  of  1802,  1803  and 
1805-1806.  That  of  1830  recurred  in  1831-1832.  Next  we  have  in 
1833  the  true  pandemic  originating  in  Russia.  Recurrences  of  the 
epidemic  of  1836-1837  were  found  in  1838  and  in  1841.  Those  spreads 
which  occurred  in  1847  and  1848  found  successors  in  the  year  1851. 
In  1890  the  influenza  outbreaks  were  as  a  rule  single  or  isolated  and 
occurred  in  only  a  few  places  of  Europe,  particularly  in  Lisbon,  Niirn- 
berg,  Paris,  Copenhagen,  Edinburgh,  Riga,  London,  etc.  It  is  re- 
ported that  there  was  an  unusually  severe  local  outbreak  in  Japan  in 
August,  1890.  In  1891  no  general  direction  of  spread  was  manifested, 
yet  in  heavily  populated  areas,  or  states  rich  in  lines  of  communication, 
especially  those  of  Europe  and  North  America,  one  could  frequently 
trace  some  definite  direction  followed  by  the  disease  within  these 
relatively  small  territories. 

A.  Netter  made  the  following  observation  at  that  time:  "La  Grippe 
a  fait  des  explosions  simultanees  ou  successives,  et  on  n'a  pu  en  aucune 
facon  subordonner  ces  differents  foyers  comme  cela  avait  ete  possible  en 
1889-90.  II  parait  y  avoir  eu  des  reveils  de  I'epidemie  sur  divers 
points." 

Leichtenstern  describes  the  subsequent  spread  of  the  disease: 
"The  transfer  of  the  disease  by  ships  which  played  such  an  important 
role  in  the  first  epidemic  appeared  to  be  insignificant  in  1891,  in  spite 
of  the  fact  that  influenza  was  present  in  many  of  the  English  colonies. 
The  third  real  epidemic  spread  of  influenza  was  a  true  pandemic  which 


46  INFLUENZA 

began  in  the  autumn  (October)  of  1891  and  lasted  through  the  whole 
winter  until  the  spring  of  1892.  It  involved  all  of  Europe  and  North 
America  and  spread  to  all  other  lands,  but  here  again  the  geographic 
distribution  followed  no  rule.  There  was  no  spread  of  influenza  from 
a  central  point,  no  continuous  spread  following  lines  of  communica- 
tion, and  there  was  no  longer  an  early  predominance  in  the  cities  lying 
on  the  lines  of  communication  or  in  the  larger  cities  and  commercial 
centers,  as  had  been  the  case  in  the  first  epidemic.  In  England  in 
1891  the  first  outbreaks  occurred  frequently  in  country  districts.  The 
epidemic  raged  nearly  four  months  in  the  northern  part  before  it 
finally  reached  London  in  May.     The  same  was  true  of  Australia. 

"One  peculiarity  of  the  recurrent  epidemic  lay  in  the  much  more 
contagious  character  of  the  disease  and  the  remarkably  greater  mortal- 
ity. In  Sheffield  the  mortality  in  the  recurrent  epidemic  was  greater 
than  in  the  pandemic,  even  though  the  epidemic  picture  was  that  of  a 
primary  wave." 

By  way  of  summary  of  our  knowledge  of  the  primary  and  secondary 
spread  in  general  up  to  the  epidemic  of  1918,  we  may  enumerate  the 
more  important  characteristics: 

1.  Occurrence  of  true  pandemics  at  wide  intervals,  primarily 
intervals  of  several  decades. 

2.  Indefinite  knowledge  and  conflicting  evidence  regarding  site 
and  manner  of  origin. 

3.  Apparent  transmission  chiefly  or  entirely  through  human 
intercourse. 

4.  Rapid  spread  over  all  countries,  the  rapidity  roughly  paralleling 
the  speed  of  human  travel. 

5.  Rapid  evolution  of  the  disease  in  the  communities  where  out- 
breaks occur,  with  nearly  equally  rapid  subsidence  after  several  weeks' 
duration. 

6.  Apparent  lack  of  dependance  on  differences  of  wind  or  weather, 
seasons  or  climate. 

7.  Generally  low  mortality  in  contrast  to  enormous  morbidity. 
Variation  in  the  incidence  of  disastrous  secondary  infections. 

8.  Tendency  to  successive  recurrences  at  short  intervals. 


AX    EPIDEMIOLOGIC    STUDY  47 

SECTION  II. 

Influenza    Epidemics  Since   1893. 

In  this  section  of  our  report  we  will  describe  with  as  great  accuracy 
as  our  sources  of  information  will  permit,  and  in  as  great  detail  as 
space  will  allow  the  events  which  have  led  up  to  the  epidemics  of 
1918-20  and  the  various  phases  of  the  epidemics  themselves.  Points 
of  similarity  with  previous  epidemics  will  be  made  obvious;  the  dif- 
ferences, when  of  significance,  will  be  described  and  studied  in  detail. 

Occurrence    Since    1893. 

Attempts  even  today  to  determine  when  and  where  influenza  has 
prevailed  in  the  world  since  the  great  pandemic  of  the  last  century  are 
met  with  great  difficulties.  There  are  several  reasons  for  this,  chief 
among  which  is  the  absence  of  definite  characteristics  by  which  the 
disease  may  be  recognized.  The  isolated  solitary  case  baffles  positive 
diagnosis.  Nearly  every  year  there  are  reports  in  the  literature  of 
small  outbreaks  in  institutions  or  communities  in  which  the  clinical 
picture  is  that  of  epidemic  influenza.  As  a  rule  the  conclusion  has 
been  in  these  cases  that  because  the  bacteriologic  findings  did  not  show 
a  predominance  of  Pfeiffer's  bacillus  the  epidemic  was  not  true  influ- 
enza. This  is  particularly  true  in  the  outbreaks  in  w'hich  the  strepto- 
coccus predominated.  Today  our  views  concerning  the  bacteriology 
have  changed  distinctly,  and  I  believe  it  is  safe  to  say  that  the  predom- 
inance of  a  streptococcus  in  a  local  epidemic  in  no  way  rules  out  influ- 
enza, and  that  the  only  criteria  by  which  we  may  judge  are  the  clinical 
picture  and  the  evidence  of  high  infectivity,  together  with  the  epidem- 
iologic characteristics  of  the  local  outbreak. 

Period  1893-1918. — A  review  of  the  medical  literature  between  1889 
and  1918  gives  one  a  certain  impression  which  may  be  summarized  as 
follows:  Between  1890  and  1900  the  disease  was  in  general  more 
highly  prevalent  in  most  localities  than  at  any  time  during  the  preced- 
ing thirty  years.  At  no  time  during  this  decade  did  the  annual  death 
rate  from  influenza  in  England  and  Wales  fall  to  anywhere  near  the 
figures  that  had  prevailed  consistently  between  1860  and  1889.  Be- 
tween 1900  and  1915  there  was  a  gradual  diminution,  but  still  not  to 
the  extent  that  had  prevailed  previous  to  1889.  Since  1915  there 
appears  to  have  been  a  gradual  increase.  During  the  entire  period 
there  has  been   difficulty  in   distinguishing  between  the  disease  in 


48  -  INFLUENZA 

question  and  other  respiratory  tract  infections,  particularly  coryza, 
sore  throat,  tonsillitis,  and  bronchitis.  Many  of  the  local  epidemics 
which  appear  probably  to  have  been  true  influenza  have  had  associated 
with  them  a  high  incidence  of  sore  throats.  We  describe  this  as 
sore  throat,  rather  than  tonsillitis,  because  the  clinician  remarks  that 
although  the  throat  is  sore  there  is  little  if  any  demonstrable  inflamma- 
tion of  the  tonsils. 

Chart  VIII  published  by  Sir  Arthur  Newsholme,  showing  the 
death  rate  per  million  of  population  from  influenza  in  England  and 
Wales  gives  some  idea  of  the  prevalence  of  the  disease  in  the  first  part 
of  the  interpandemic  period  in  those  countries.  It  should  be  remarked 
that  the  record  is  for  deaths  from  influenza  only. 

For  records  in  this  country  it  is  convenient  to  refer  to  the  death 
rate  in  the  State  of  Massachusetts;  first,  because  the  records  in  that 
State  have  been  carefully  kept  for  a  long  period;  and  second,  because 
influenza  has  been  carefully  studied  in  this  State  during  both  epidemics 
by  two  most  competent  epidemiologists.  For  the  period  preceding 
1889  we  quote  herewith  from  Abbott: 

"For  the  past  45  years  or  more,  or  during  the  period  of  registrar 
tion  which  began  with  the  year  1842,  no  epidemic  of  influenza  has 
prevailed  within  the  State  to  such  an  extent  as  to  have  manifested 
itself  in  any  serious  manner  in  the  annual  lists  of  deaths.  An  examin- 
ation of  the  registration  reports  for  each  year  since  1842  shows  that 
in  no  year  were  recorded  more  than  100  deaths  from  this  cause;  the 
highest  number  from  influenza  in  a  single  year  (92)  occurred  in  1857, 
and  the  least  number  (8)  in  1884.  The  average  annual  number  of 
deaths  from  this  cause  reported  in  the  State  for  the  period  1842  to  1888 
was  38.  The  average  number  during  the  first  half  of  this  period  was 
greater  than  that  of  the  last  half,  especially  when  considered  with 
reference  to  the  increase  of  population.  From  these  statistics  of  non- 
epidemic  influenza  between  the  years  1842  and  1888  it  appears  that  its 
greatest  prevalence,  or  rather  the  years  in  which  the  mortality  from 
this  cause  was  greatest,  were  also  years  of  unusual  mortality  from 
pneumonia,  and  in  some  instances  from  bronchitis." 

Frost  has  charted  the  death  rate  per  100,000  from  influenza  and 
from  all  forms  of  pneumonia  in  Massachusetts  by  month,  from  1887 
to  1916.  From  it  he  concludes  that  the  epidemic  of  1889-1892 
developed  in  three  distinct  phases,  the  first  culminating  in  January, 
1890,  the  second  in  April  and  May,  1891,  and  the  third  in  January, 
1892.  The  mortahty  was  higher  in  1891  than  in  1890,  and  still  higher 
in  1892,  while  in  1893,  although  there  was  no  distinct  epidemic,  the 


CHART  VIII. 


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Death    rates    per    million    from    influenza    in    England  and   Wales,  frpm   1845  to   1917. 
{N  ewsholme.) 


CHART  IX. 


I 


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1897      1688    1699     1890     I69(       1892     \i333     I^S'^      '895    1996 


1637     18^8       l8Sg       1900       laUl        (902       ISOS      I9Q1      I'SOb        I5a6 


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1907        ;eU8      [909     jgiO        i3ll 


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-  Monthly  death  rates  per  100,000  from  influenza  and  from  pneumonia  in  Massa- 
chusetts from  1887  to  1916.     (Frost.) 


CHART  X. 


800 

500 
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200 
lOQ 


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Monthly  death  rates  per  100,000  from  influenza  and  pneumonia  in  three  cities 
of  the  United  States  from  1910  to  1918,  inclusive.     {Frost:) 


AN    EPIDEMIOLOGIC   STUDY  49 

pneumonia  mortality  for  the  year  was  even  higher  than  that  of  1892. 
Frost  remarks  that  this  corresponds  to  the  experience  in  England, 
and  that  it  apparently  represents  the  general  experience  in  other 
countries  (see  charts  IX  and  X). 

In  the  absence  of  comparable  statistics  for  Massachusetts  in  1917 
and  1918,  Frost  has  studied  for  those  years  certain  other  localities, 
particularlj^  Cleveland,  San  Francisco  and  New  York  City.  The 
mortality  in  all  of  these  places,  as  well  as  in  Massachusetts,  was  fairly 
regular  from  1910  to  1915,  but  in  December  of  the  latter  year  and 
January  of  1916  there  occurred  in  New  York  and  Cleveland  a  sudden 
sharp  rise  in  mortality.  This  was  not  shown  distinctly  in  the  San 
Francisco  curve,  but  it  was  a  rise  which  was  almost  universal  and 
synchronous  over  the  entire  registration  area.  It  is  of  interest  as 
indicating  the  operation  of  some  definite  and  widespread  factor,  and 
suggesting  in  this  group  of  diseases  an  epidemic  tendency  which  is 
perhaps,  as  Frost  remarks,  not  sufficiently  appreciated.  In  January 
of  1916  he  found  that  influenza  was  reported  to  be  epidemic  in  twenty- 
two  states,  including  all  sections  of  the  country.  The  epidemic  was 
very  mild.  In  the  early  spring  of  1918  there  was  another  sharp  rise, 
which  we  shall  discuss  in  greater  detail  later. 

Increase  in  1900-1901. — Reference  to  Frost's  chart  for  Massachu- 
setts shows  that  there  was  also  a  rise  in  the  curve  around  1900.  At 
this  time  influenza  was  quite  widely  disseminated.  Early  in  1901  the 
Marine  Hospital  Service  made  a  canvass  of  all  the  states  and  several 
foreign  countries  to  determine  the  epidemic  prevalence  of  influenza. 
The  results  of  the  canvass  were  published  in  the  Public  Health  Reports. 
The  records  lack  the  detail,  particularly  in  the  description  of  clinical 
symptoms,  that  is  desirable  in  arriving  at  an  identification,  but  the 
universal  agreement  from  all  individuals  reporting,  in  the  com- 
paratively high  morbidity  and  remarkably  low  mortahty,  together 
with  the  widespread  distribution,  and  the  duration  of  the  local  epidemic 
leaves  little  doubt  as  to  the  identity. 

Influenza  was  reported  present  in  October  of  1900  in  Los  Angeles, 
Milwaukee  and  New  Orleans.  In  November  it  became  prevalent  in 
Toledo  and  Cincinnati  and  in  New  York  City.  In  December  the 
disease  was  present  in  Chicago,  Albany  Philadelphia,  San  Francisco, 
Denver,  Baltimore,  Grand  Rapids,  Columbus,  O.,  Portland,  Me., 
Detroit,  Albuquerque  and  Omaha.  In  January  it  was  reported  in 
New  Haven,  Boston,  Washington,  D.  C,  Indianapohs,  Louisville, 
Ky.,  Wilmington,  Del.,  Portland,  Ore.,  and  Juneau,  Alaska. 

Although  the  disease  was  mild,  in  some  locaHties  a  high  proportion 


50  INFLUENZA 

of  the  population  was  attacked.  Thus  in  New  Haven  it  was  estimated 
that  10  per  cent,  developed  the  disease,  and  in  Los  Angeles  20  per  cent., 
while  in  Wilmington,  40,000  were  estimated  to  have  become  ill.  In 
certain  small  towns  in  Texas  the  incidence  was  especially  high.  In 
Pittsburgh,  Texas,  ten  per  cent;  Laredo,  15  to  20  per  cent.;  Hearne, 
50  per  cent. ;  and  El  Paso,  50  per  cent,  were  attacked.  The  duration 
of  the  epidemic  in  most  localities  was  from  four  to  six  weeks. 

Thus  we  see  that  in  October,  November  and  December  of  1900  and 
January  of  1901  there  was  a  widespread  epidemic  affecting  all  parts  of 
the  United  States.  Many  additional  records  in  the  Public  Health 
Reports  coming  from  small  towns  have  not  been  included  in  this 
summary. 

At  the  same  time  an  attempt  was  made  to  determine  the  prevalence 
in  foreign  countries  and  letters  were  sent  to  the  various  United  States 
Consulates.  It  was  discovered  that  the  disease  was  mildly  epidemic 
in  Denmark  in  October,  in  Berlin  in  November,  in  Cuba,  British 
Columbia,  Ontario,  Egypt,  Paris,  Mexico  and  the  West  Indies  in 
December;  in  Flanders,  Porto  Rico,  Honolulu,  in  January  of  1901;  in 
Malta  in  February,  1901 ;  and  in  London  and  Ireland  in  March  of  that 
year.  The  following  countries  reported  that  they  had  no  influenza 
at  the  time:  Windward  Islands,  Jamaica,  Bahamas,  Brazil,  India, 
Colombia,  Costa  Rica,  Ecuador,  Honduras,  Persia,  Philippine  Islands, 
Spain,  Switzerland.  The  disease  was  reported  as  being  not  of  epi- 
demic prevalence  in  the  following  localities :  Marseilles,  Paris,  Bremen, 
Hamburg,  Mainz,  Stuttgart,  Bristol,  London,  Liverpool,  England  as 
a  whole,  Scotland,  Amsterdam,  Naples,  Constantinople. 

Reports  from  Switzerland  and  from  Brazil  stated  that  there  had 
been  no  influenza  since  the  pandemic  period  1889-1893.  The  death 
rate  per  100,000  in  Glasgow  from  influenza  for  1896  was  recorded  as 
six;  for  1897,  twelve;  for  1898,  fifteen;  1899,  twenty-two  and  for  1900, 
twenty-seven. 

The  disease  was  present  in  Lima,  Peru  in  March,  1900,  and  at  Malta 
in  the  same  month.  In  Prague  it  was  stated  that  ten  per  cent,  of  the 
population  had  been  attacked  in  the  winter  of  1901 .  In  Sivas,  Turkey, 
fifty  per  cent,  of  a  population  of  50,000  were  estimated  to  have  been 
taken  ill  within  the  winter  months.  It  was  reported  from  Valencia, 
Spain,  that  there  had  been  four  or  five  visitations  of  influenza  since 
the  preceding  pandemic,  each  recurring  invasion  presenting  a  milder 
and  less  expansive  form  than  its  predecessor.  Very  few  deaths  had 
been  recorded  as  directly  due  to  influenza,  but  an  increased  mortality 
followed  the  epidemics.  In  normal  times  the  average  mortality  was 
ninety  deaths  per  week.     After  a  visitation  of  influenza  the  number 


AN    EPIDEMIOLOGIC    STUDY  51 

had  increased  to  as  much  as  160  per  week.     The  population  numbered 
204,000. 

Period  from  1901  to  1915. — Between  1900,  with  its  wide  distribution 
of  a  very  mild  influenza,  and  1915,  there  is  very  little  mention  of 
epidemic  prevalence  of  the  disease.  References  which  appeared  in  the 
Public  Health  Reports  during  the  interval  are  characterized  chiefly 
by  their  brevity,  and  by  the  absence  of  descriptive  detail.  They 
should  nevertheless  be  included. 

In  October  of  1901  there  was  some  increase  of  the  disease  in  the 
Hawaiian  Islands,  110  cases  being  reported  on  the  island  of  Kauai. 

At  the  same  time,  C.  Williams  Bailey  reported  a  mild  form  of 
influenza  existing  in  Georgetown,  S.  C,  which  was  first  considered  to 
be  hay  fever  in  consideration  of  the  presence  of  the  rice  harvest  season, 
but  which  was  finally  decided,  after  careful  investigation,  to  be  true 
influenza. 

On  July  21,  1902,  the  U.  S.  Consul  at  Canton,  China,  telegraphed 
that  influenza  "was  almost  epidemic,  plague  sporadic  in  Canton." 

In  1903  the  disease  was  reported  as  apparently  prevalent  at  New 
Laredo,  Texas. 

Surgeon  Gassaway,  of  the  Marine  Hospital  Service,  reported  from 
Missouri,  December  14,  1903,  as  follows:  "There  is  a  very  decided 
increase  in  the  number  of  cases  of  influenza  in  this  vicinity.  Two 
have  been  admitted  within  the  last  few  days  to  this  hospital,  and 
several  cases  have  appeared  among  the  patients  under  treatment. 
In  these  cases  the  onset  is  sudden  and  the  disease  appears  principally, 
at  least  at  first,  to  be  confined  to  the  nose  and  throat." 

Measles  and  influenza  were  reported  prevalent  in  Barbados,  West 
Indies,  during  the  month  of  December,  1904. 

Sturrock  describes  a  quite  typical  local  epidemic  in  a  British 
institution  in  1905. 

Influenza  was  epidemic  in  Guayaquil  and  various  other  places  in 
Ecuador  during  the  months  of  June  and  July,  1906. 

Selter  speaks  of  a  true  local  epidemic  of  a  disease  clinically  resem- 
bling influenza  which  occurred  in  1908  and  extended  over  the  territory 
from  France  to  the  Rhine. 

Hudeshagen  mentions  having  examined  bacteriologically  cases  of 
influenza  in  the  year  1914. 

Ustvedt  relates  his  experience  at  the  Ullevaal  Hospital  up  to 
September,  1918.  Since  1890  there  had  been  cases  reported  every 
year  from  the  high  marks  of  10,461  cases  in  Christiania  in  1890  and 
5,728  in  1901  to  the  lowest  figure,  138  in  1906.  "The  cases  listed  as 
influenza  in  the  last  few  years  may  have  been  merely  a  catarrhal  fever. 


52  -  INFLUENZA 

This  is  the  more  probable  as  the  cases  were  restricted  to  the  winter 
months,  while  influenza  usually  occurs  at  other  seasons." 

Jundell  believes  that  influenza  is  endemic  at  Stockholm,  Sweden, 
hundreds  of  cases  being  reported  there  each  year.  During  the  years 
1912-1919  Pfeiffer's  bacillus  has  been  found  in  ten  per  cent,  of  those 
cases  in  which  the  diagnosis  seemed  certain. 

A  current  comment  in  the  Journal  of  the  American  Medical 
Association  in  1912  remarks  that  epidemics  of  coryza,  sore  throat, 
and  bronchitis  usually  have  been  called  influenza  or  grip  because  of  the 
characteristic  contagiousness  and  the  infectivity,  the  persistence  of 
the  symptoms,  and  the  tendency  to  prostration  and  mental  depression. 
But  this  diagnosis  has  not  been  satisfactorily  confirmed  by  bacteri- 
ologists. An  epidemic  according  to  the  Journal,  which  occurred  in 
Boston  and  which  was  called  sore  throat,  was  studied  by  Richardson 
and  others.  They  traced  the  contagion  to  a  streptococcus  which 
apparently  was  spread  by  means  of  milk.  Mtiller  and  Seligman  had 
recently  carried  out  a  study  of  an  influenza  epidemic  among  children 
in  Berlin  and  concluded  that  the  causative  organism  was  a  strepto- 
coccus, differing  so  much  from  the  ordinary  germ  that  they  used  the 
term  "grip  streptococcus."  Davis  and  Rosenau,  according  to  the 
comment,  had  made  a  bacteriologic  study  of  a  recent  epidemic  of  sore 
throat  in  Chicago,  and  had  demonstrated  as  the  exciting  agent  a 
streptococcus  of  peculiar  characteristics,  which  in  many  respects 
resembled  the  organism  described  by  Mtiller  and  Seligman.  The 
Journal  noted  that  these  three  epidemics  occurring  during  the  years 
1911  and  1912  in  widely  separated  communities  were  all  caused  by  the 
streptococcus,  and  cautioned  against  the  proneness  to  call  all  such 
epidemics  grip.  Today  the  predominance  of  the  streptococcus  would 
not  necessarily  rule  out  influenza  in  our  minds. 

In  the  winter  of  1913,  C.  L.  Sherman  had  occasion  to  study  care- 
fully fourteen  cases  of  so-called  influenza  in  the  vicinity  of  Luverne, 
Minnesota.  Bacteriologic  smears  and  cultures  were  made  from  the 
throat  and  sputum  in  all  cases.  Bacillus  influenzae  was  found  in 
two  of  the  fourteen;  pneumococcus  in  four  and  streptococcus  in  all. 
Tubercle  bacilli  were  found  in  one  case.  The  onset  of  the  disease  was 
invariably  abrupt.  The  fever  in  all  cases  ranged  between  101°  and 
104°;  symptoms  indicative  of  infection  of  the  upper  respiratory  tract 
were  always  present.  There  was  more  or  less  sore  throat  in  all. 
There  was  either  cough  at  the  onset  or  else  it  appeared  within  48 
hours.  Headache  was  complained  of  by  twelve  of  the  fourteen;  pains 
in  the  back  and  in  the  limbs  by  thirteen,  and  nervous  symptoms  by 


AN    EPIDKMIOLO(;iC    STUDY  53 

six.  Prostration  out  of  all  proportion  to  the  fever  and  other  symptoms 
prevailed.  Two  developed  an  otitis  media  and  the  streptococcus  was 
isolated  from  the  purulent  discharge  in  both  cases.  One  patient  had  a 
complicating  empyema,  and  one  an  acute  arthritis.  Sherman  also 
concluded  that  we  are  prone  to  call  too  diverse  diseases  influenza. 

Walb  stated  in  1913  that  at  Bonn  during  the  preceding  years  there 
had  been  numbers  of  cases  of  a  febrile  affection  which  seemed  to 
be  typical  influenza,  but  for  which  the  pneumococcus  appeared  to  be 
responsible.  They  were  never  able  to  isolate  the  influenza  bacillus, 
and  according  to  their  statement  the  Hygienic  Institute  at  Bonn,  as 
well  as  that  at  Berlin,  had  not  "encountered  an  influenza  bacillus 
within  the  preceding  ten  years." 

C.  T.  Mayer  described  in  1913  a  case  of  influenza  in  Buenos  Ayres 
which  is  of  particular  interest  in  view  of  one  of  the  symptoms,  cyanosis, 
which  was  so  prominent  a  feature  in  1918.  This  appears  to  have  been 
an  isolated  case.  The  diagnosis  wavered  between  miliary  tuberculosis 
and  pneumonic  plague,  because  of  the  high  fever  and  intense  cyanosis, 
with  nothing  to  explain  the  cyanosis  on  the  part  of  the  heart.  There 
were  signs  of  severe  congestion  of  both  lungs,  and  notable  enlarge- 
ment of  the  spleen.  Bacteriologic  examination  w^as  negative  except 
for  the  presence  of  Bacillus  influenzae  and  Micrococcus  catarrhalis. 
The  patient  subsequently  improved  rapidly,  and  the  lungs  were 
entirel}"  normal  after  thirty  days,  thus  iiiling  out  the  other  two 
diseases. 

A  London  letter  to  the  Journal  of  the  American  Medical  Association 
dated  February  5,  1915,  runs  as  follows: 

"Since  the  outbreak  of  the  war  the  pubUc  health  has  been  remark- 
ably good,  but  the  record  is  now  being  threatened  in  the  case  of 
London,  at  any  rate,  by  an  epidemic  of  influenza. 

"The  gastric  symptoms  which  distinguished  last  year's  epidemic 
are  absent.  The  disease  is  most  infectious.  Whenever  it  has  seized 
the  individual  it  has  usuallj^  run  through  the  entire  household. 

"Whole  offices  have  succumbed,  and  as  the  mildness  of  the  attack 
lures  the  sufferer  to  continue  his  normal  occupation,  the  disease  has  a 
full  opportunity  of  extending.  A  large  number  have  resulted  in 
pleuro-pneumonia;  otherwise  the  chief  sj-mptoms  are  headache,  fever, 
tonsillitis." 

TeUing  and  Hann  describe  another  clinical  diagnosis  of  influenza, 
the  diagnosis  being  concurred  in  by  Sir  James  Goodhart  and  Sir 
Clifford  Allbutt.  The  onset  was  absolutely  sudden  at  a  supper  party 
on  November   10,   1912.     The  patient  had  a  shght  rigor,  and  was 


54  INFLUENZA 

compelled  to  go  to  bed.  In  the  night  he  had  a  longer  and  more 
severe  rigor,  with  a  temperature  of  103°.  On  the  following  morning 
he  dressed,  but  another  chill  sent  him  back  to  bed  with  a  temperature 
still  103°,  pulse  110,  regular,  and  remarkably  dicrotic.  There  was  no 
cough  and  no  sore  throat.  Another  chill  occurred  in  the  evening. 
On  November  12th  the  patient  had  two  chills,  the  temperature  remain- 
ing steadily  at  103°  to  104°.  The  patient  complained  much  of  nausea 
but  did  not  vomit.  On  November  13th  the  temperature  remained 
up,  there  was  no  chill  on  this  day;  the  spleen  was  large  and  easily  felt 
for  the  first  time.  On  the  14th  note  was  made  that  there  was  no 
headache.  On  the  15th,  16th  and  17th  the  temperature  began  to 
fluctuate.  On  the  18th  there  were  two  severe  rigors,  and  by  the  19th 
the  temperature  suddenly  fell  to  normal,  with  drenching  sweat. 
Throughout  there  was  nothing  to  suggest  pneumonia,  and  typhoid 
fever  appears  to  have  been  successfully  ruled  out. 

An  epidemic  of  influenza  which  prevailed  in  the  city  of  Pittsburgh, 
Pennsylvania,  from  December  to  February  of  1907  and  1908,  has  been 
described  by  J.  A.  Lichty.  He  says  that  the  epidemic  was  as  wide- 
spread, though  probably  not  quite  as  severe,  as  the  pandemic  of 
1889.  Whole  families,  including  servants  and  all  associated  with 
the  household,  were  afflicted  in  rapid  succession.  The  onset  was 
sudden  and  severe,  the  usual  symptoms  of  pain,  all  over,  being  most 
pronounced.  The  temperature  did  not  go  unusually  high,  nor  did  it 
seem  to  be  in  accord  with  the  severity  of  the  symptoms  when  the 
patient  took  to  his  bed.  In  typical  cases  the  attack  lasted  from  two  to 
three  or  four  days.  Peculiar  to  this  epidemic  seemed  to  be  the  general 
complaint  of  sore  throat.  Upon  examination  the  throat  rarely  showed 
any  other  evidence  of  an  abnormal  condition  than  a  rather  dark 
cyanotic  blush,  which  was  most  intense  over  the  tonsils  and  faded  out 
over  the  roof  of  the  mouth.  This  was  rarely  associated  with  any 
swelling  or  fever.  Sinusitis  and  otitis  media  seem  to  have  been  the 
two  most  frequent  complications.  The  disease  appeared  to  be 
particularly  fatal  for  chronic  invalids.  It  was  highly  contagious. 
Many  of  those  physicians  who  were  frequently  exposed  to  the  disease 
fell  victims. 

At  the  same  time  C.  H.  Jones  described  an  epidemic  of  the  same  dis- 
ease in  Baltimore.  The  symptoms  were  described  as  headache, 
backache,  limbache,  with  a  slight  elevation  of  temperature,  seldom 
more  than  102°.  Catarrhal  symptoms  developed  secondarily  and 
were  not  so  prominent  a  feature  as  in  former  epidemics.  There  were 
some  gastric  symptoms,  usually  consisting  of  vomiting  and   nausea. 


AX    EPIDEMIOLOGIC    STUDY 


55 


Jones  quotes  no  statistics,  but  feels  sure  that  the  infection  was  more 
extensive  than  at  any  period  since  1895. 

Coakley  and  Dench  describe  throat  and  ear  complications  as  they 
saw  them  in  New  York.  From  this  we  may  assume  that  the  disease 
was  present  at  the  same  time  in  New  York  City. 

The  following  chart,  derived  from  the  U.  S.  Vital  Statistics  Report 
shows  the  increase  in  the  death  rates  from  influenza  in  1900  and  1901 ; 
that  of  1907  and  1908,  and  finally  an  increase  to  26.4  per  100,000  in 
1916,  which  reflects  the  epidemic  beginning  in  the  latter  part  of  1915: 


Influenza  and  Pneumonia  Mortality  in  the  United  States  Registration  Area  for  Each 

Year  Since  1900. 


Year 

Annual  death  rates  per  100,000. 

Pneumonia. 

Influenza.               1      Combined  diseases. 

1900 

158.6 

22.8 

181.4 

1901 

133.5 

32.2 

167.7 

1902 

124.7 

10.1 

134.8 

1903 

122.6 

18.5 

141.1 

1904 

136.3 

20.2 

156.5 

1905 

115.7 

18.8 

134.5 

1906 

110.8 

10.3 

121.1 

1907 

120.8 

23.3 

144.1 

1908 

98.8 

21.3 

120.1 

1909 

96.3 

13.0 

109.3 

1910 

147.7 

14.4 

162.1 

1911 

133.7 

15.7 

149.4 

1912 

132.3 

10.3 

142.6 

1913 

132.4 

12.2 

144.6 

1914 

127.0 

9.1 

136.1 

1915 

132.7 

16.0 

148.7 

1916 

137.3 

26.4 

163.7 

At  best  our  information  for  these  years  is  unsatisfactory.  It  is 
greatly  to  be  desired  that  individuals  who  have  access  not  only  to  the 
current  medical  Hterature,  but  also  to  the  vital  statistics  and  other 
records  for  all  countries  possessing  reliable  records,  and  who  are 
versed  in  the  newer  mathematical  methods  of  demography,  estabhsh 
definitely  the  influenza  prevalence  and  distribution  during  these  inter- 
pandemic  years.  The  difficulty  in  this  work  is  that  mortality  statistics 
are  unreliable  and  morbidity  statistics  are  lacking. 

Influenza  in  1915-1916. — Until  the  end  of  1915  there  was  no  wide- 
spread distribution  in  the  United  States  similar  to  that  of  1900  and 
1901,  but  at  that  time  there  developed  a  widespread  epidemic  in  this 


56 


INFLUENZA 


country  of  similar  or  possibly  slightly  greater  severity  than  that  of 
fifteen  years  previously.  Reference  to  the  last  table  will  show  that 
during  1916  the  annual  death  rate  from  influenza  as  reported  in  the 
United  States  Vital  Statistics  reached  the  rate  of  26.4  per  100,000. 
According  to  V.  C.  Vaughan  the  literature  of  that  time  shows  that  this 
epidemic  originated  in  the  West,  first  attracting  attention  at  Denver, 
and  gradually  spread  over  the  country. 

Dr.  Dublin  of  the  Metropolitan  Life  Insurance  Company  gives  the 
following  table  in  which  the  deaths  from  influenza  and  pneumonia 
during  the  months  of  December,  1914,  and  January,  1915,  are  com- 
pared with  deaths  from  the  same  cause  during  the  months  of  December, 
1915,  and  January,  1916: 


Name  of  city 


Deaths  reported  as  due  to 
influenza. 


In  1915-16. 


In  1914-15. 


Deaths  reported  as  due  to 
pneumonia. 


In  1915-16.         In  1914-15. 

i ' . 


Baltimore 

Cincinnati 

New  Orleans 

New  York 

57 

81 

97 

494 

324 

38 

1,091 

12 

2 

44 

62 

62 

3 

185 

^19 

105 

35 

2,067 

564 

31 

3,021 

101 

84 

29 

1,207 

272 

31 

Philadelphia 

Providence 

Total 

1,724 

DubUn  states  that  the  Industrial  Department  of  the  Metropolitan 
Life  Insurance  Company,  covering  the  entire  country  and  embracing 
ten  millions  of  people,  had  deaths  in  the  periods  above  mentioned,  as 
follows : 

In  December,  1914,  and  January,  1915,  the  number  of  deaths  attributed  to 

influenza  was 165 

While  in  the  corresponding  months  of  1915-1916  the  deaths  attributed  to 

influenza  were 957 

The  deaths  attributed  to  pneumonia  in  December,  1914,  and  January,  1915, 

were : 1,468 

While  the  number  of  deaths  attributed  to  the  same  cause  in  December,  1915, 

and  January,  1916,  were 2,563 

Coffey  and  others  have  reported  an  epidemic  of  influenza  at  Worces- 
ter, Mass.  during  the  first  three  weeks  of  January,  1916.  During  the 
first  three  weeks  of  January,  1915,  there  were  reported  in  that  city 
twenty-two  deaths  from  respiratory  diseases,  making  a  total  of  14.9 
per  cent,  of  the  total  deaths.  In  the  same  period  of  1916  there  were 
reported  ninety-three  deaths  from  acute  respiratory  diseases  in  the 
same  population. 


AX    EPIDEMIOLOGIC    STUDY  O/ 

Two  of  the  more  complete  descriptions  of  the  epidemic  of  the  year 
1915-16  are  those  by  Mathers,  and  by  C'apps  and  Moody.  Mathers 
reports  that:  "Durinf?  the  winter  of  1915-1910  the  United  States 
was  visited  by  a  severe  epidemic  of  acute  respiratory  infections  which 
resembled  in  every  detail  the  great  epidemic  of  1890.  This  outbreak 
was  apparently  first  noticed  in  the  Middle  Western  States,  and  it 
spread  rapidly  over  the  entire  country,  taking  a  heav}-  toll  of  human 
life.  December  and  January  were  the  months  in  which  these  infections 
were  most  prevalent,  and  the  epidemic  had  almost  completely  lost  its 
impetus  by  March,  1916.  During  the  height  of  this  epidemic  in 
Chicago,  sixtj'-one  cases  of  the  disease  were  studied  bacteriologically, 
and  the  results  form  the  basis  of  this  paper." 

Mathers  found  hemolytic  streptococci  in  forty-six  instances,  in  all 
of  which  they  predominated.  Green  producing  streptococci  were 
found  thirty  times,  with  one  pure  culture,  and  pneumococci  thirty 
times  with  four  pure  cultures.  Staphylococci  were  isolated  in  fifty 
cases;  Micrococcus  catarrhalis  in  six,  and  Friedlander's  bacillus  in  one 
case.  The  influenza  bacillus  was  found  in  only  one  instance,  and  then 
in  small  numbers.  The  majority  of  the  patients  were  studied  earh- 
in  the  course  of  the  disease,  and  in  the  earliest,  hemolytic  streptococci 
were  almost  constantly  found,  especially  in  the  throat.  In  the  atypical 
pneumonia  which  followed  many  of  the  attacks  of  grip,  hemolytic 
streptococci  predominated.  In  none  of  these  was  the  Bacillus  influ- 
enza found. 

Mathers  reported  that  coincident  wdth  the  epidemic  among 
humans  there  was  an  epizootic  of  so-called  influenza  among  horses. 
The  symptoms  are  very  similar  to  that  of  the  disease  among  humans. 
He  isolated  a  streptococcus  as  the  predominating  organism  in  the 
horses.  The  streptococci  from  human  and  equine  sources,  although 
similar  in  many  characteristics,  differed  widely  in  pathogenicity,  and 
seemed  to  be  highly  parasitic  for  the  specific  hosts. 

Capps  and  ^Moody  found  that  in  man  most  cases  began  rather 
abruptly,  with  corj^za,  phary^ngitis,  larj-ngitis,  or  bronchitis. 

"The  chief  complications  were  inflammation  of  the  accessor}'  si- 
nuses of  the  head,  and  bronchopneumonia,  the  latter  being  responsible 
for  most  of  the  fatalities.  None  of  these  symptoms  taken  alone  would 
justify  the  distinctive  name  of  grip.  But  the  widespread  and  almost 
simultaneous  onset  of  this  fairly  uniform  symptom  group  and  the 
rapid  cessation  of  the  epidemic  after  a  few  weeks  reminded  physicians 
generally  of  the  great  grip  pandemic  of  1889-1890.  This  resemblance 
was  further  strengthened  by  the  unusual  prostration  lasting  days  or 


58  INFLUENZA 

weeks  after  even  mild  attacks.  The  older  practitioners  can  recall  no 
similar  epidemic  during  the  twenty-five  years  intervening  between 
1890  and  this  year.  The  numerous  epidemics  of  septic  sore  throat 
have  all  been  entirely  different  in  their  symptomatology,  and  all  were 
restricted  to  certain  localities.  The  term  "grip,"  therefore,  seems 
justified  from  a  clinical  standpoint. 

"The  public  health  reports  offer  evidence  of  an  unusual  prevalence 
of  pneumonia  in  the  larger  cities.  Nicolas  calls  attention  to  the  fact 
that  the  incidence  of  grip  was  greatest  in  those  cities  in  which  the 
mortality  from  pneumonia  was  most  strikingly  increased." 

Capps  and  Moody  found  that  as  a  rule  the  white  blood  counts 
in  the  individuals  sick  with  influenza  were  10,000  or  less.  A  number 
showed  true  leucopenia.  Less  frequently  there  was  a  leucocytosis 
up  to  15,000  or  higher. 

Influenza  between  1916  and  1918. — Zinsser  cites  Dr.  George  Draper, 
who  believes  that  he  observed  at  Fort  Riley  in  the  winter  of  1917 
epidemic  cases  of  influenza.  He  believes  that  for  Europe  too  there  is 
evidence  that  influenza  was  endemic  during  the  years  preceding  the 
great  outbreak,  and  that  a  number  of  minor  epidemic  explosions  had 
occurred  in  the  years  just  preceding  1918; 

"MacNeal  who  has  investigated  military  reports  particularly,  states 
that  small  epidemics  occurred  in  the  British  Army  in  1916  and  1917.  A 
chart  constructed  by  him  from  the  American  Expeditionary  Force 
reports  shows  that  a  considerable  rise  in  reported  influenza  cases  took 
place  in  November  and  December,  1917,  and  in  January,  1918,  gradually 
declining  toward  spring.  MacNeal,  compiling  the  data  available  in 
the  office  of  the  Chief  Surgeon.  A.  E.  F.,  states  that  the  influenza 
morbidity  reported  per  100,000  for  succeeding  months  in  1917,  were  as 
follows : 

July 321 

August 438 

September 404 

October 1,050 

November 1,980 

December 2,480 

"Robertson,  who  studied  many  of  the  secondary  pneumonias 
which  came  to  autopsy  at  this  time  found  an  unusual  type  of  lobular 
pneumonia  in  which  Pfeiffer  bacilli  were  frequently  found.  In  many 
of  these  cases  the  organisms  could  be  obtained  from  the  nasal  sinuses 
and  antra.  Similar  findings  were  reported  by  British  bacteriologists 
(Hammond,  Rolland  and  Shore,  and  Abrahams,  Hallows,  Eyre  and 


AN    KPIDEMIOLOGIC    STUDY  59 

French),  who  studied  the  cases  that  occurred  in  the  reports  by  Austrian 
phj'sicians  in  reference  to  outbreaks  of  typical  influenza  on  the  Austro- 
Russian  front  early  in  1917. 

"There  seems  little  doubt,  therefore,  that  for  some  years  before 
the  pandemic  of  1918  influenza  was  endemic  in  many  parts  both  of 
Europe  and  of  America.  As  early  as  1915-1916  Frost  finds  evidences 
of  limited  epidemic  outbreaks  in  the  United  States.  During  the 
winter  immediately  preceding  the  true  beginning  of  the  pandemic 
small  outbreaks  occurred  among  the  allied  troops  in  France,  the 
British  troops  in  England  and  probably  among  American  troops 
gathered  in  home  concentration  camps  as  well.  MacNeal  in  a  sum- 
mary of  the  conditions  prevailing  among  American  troops  in  France 
concludes  that  epidemic  influenza  in  that  country  originated  from 
the  endemic  foci  there  existing,  and  that  the  disease  was  probably 
carried  from  Europe  to  the  United  States  by  shipping.  The  former 
assumption;  namely,  that  the  epidemic  occurrence  of  the  disease  may 
have  been  due  to  the  fact  that  an  enormous  and  concentrated  newly 
introduced  material  of  susceptibles  may  have  been  Lighted  into  flame 
at  the  numerous  endemic  smoulders,  may  well  be  correct.  The  latter, 
however,  concerning  the  transportation  of  the  disease  from  Europe  to 
America  may  justly  be  questioned.  For,  in  the  first  place,  Frost's 
studies  have  shown  that  prepandemic  outbreaks  were  quite  as  frequent 
in  the  United  States  as  in  Europe  during  1915  and  1916,  and,  though 
we  have  no  proof  of  this,  there  is  reason  to  beheve  that  influenza  was 
prevalent  in  concentration  camps  during  1917." 

Carnwath,  after  remarking  that  the  epidemic  began  in  the  British 
Army  in  France  in  April,  1918,  says  that  according  to  the  reports  of 
the  Influenza  Committee  of  the  Advisory  Board  this  was  not  the  first 
time  that  Pfeiffer's  bacillus  had  appeared  in  the  armies.  On  the 
contrary,  it  had  frequently  been  found  in  cases  of  bronchopneumonia, 
especially  during  the  winter  of  1916-1917.  It  is  doubtful,  however, 
whether  much  importance,  from  the  epidemiologic  point  of  view, 
attaches  to  these  sporadic  findings  of  the  Pfeiffer  bacillus. 

Influenza  was  reported  in  the  year  1917,  but  this  year,  as  well  as 
the  epidemic  of  1916,  becomes  involved  in  a  determination  of  the  date 
of  onset  of  the  great  pandemic  of  1918. 

The  Pandemic  of  1918. 

The  date  and  site  of  onset  of  the  great  pandemic  are  subjects  con- 
cerning which  there  is  no  conclusive  information.  There  have  been 
small  outbreaks  of  clinical  influenza  with  epidemic  tendencies  at  one 


60  INFLUENZA 

place  or  another  during  nearly  all  of  the  intervening  years  since  1889. 
In  all  of  them  the  question  is  open  as  to  whether  they  were  true  influ- 
enza, and  also  assuming  that  some  were  true  influenza,  how  many  of 
them  should  be  so  included.  There  are  some  who  believe  that  the 
increase  of  morbidity  following  the  measles  epidemic  in  the  United 
States  Army  camps  in  the  winter  of  1917-18  is  genetically  associated 
with  the  great  pandemic.  In  short,  there  is  no  one  point  in  the  last 
few  years  at  which  we  may  say  that  influenza  which  had  previously 
been  non-existent  started  at  a  focus  and  spread  throughout  the  world. 

It  follows  from  the  experience  of  1889  that  we  should  at  least 
attempt  to  find  an  endemic  focus  and  to  follow  the  progression  of  the 
disease.  It  is  safe  to  say  that  once  having  become  pandemic  the 
disease  spread  as  it  did  thirty  years  previously.  Experience  in  this 
country,  where  the  autumn  spread  began  in  the  New  England  States 
and  continued  West  and  South;  knowledge  of  the  late  spread  to  remote 
localities;  the  fact  that  the  disease  first  appeared  in  England,  etc.  in 
sea  coast  towns;  the  introduction  of  the  influenza  into  new  countries  at 
seaport  towns,  after  the  arrival  of  infected  ships,  all  coincide  well  with 
the  past  history. 

But  which  of  the  several  local  epidemics  of  the  preceding  years  was 
the  direct  progenitor  of  the  great  pandemic?  In-order  to  follow  more 
clearly  the  development  of  the  facts  we  will  record  here  the  various 
hypotheses  that  will  come  up  for  consideration  as  to  the  site  of  origin 
of  the  disease. 

1.  Influenza  is  endemic  in  some  one  locality,  such  as  Turkestan 
in  Asia,  from  which  place  the  disease  spreads  throughout  the  earth 
at  intervals,  after  having  acquired  in  some  way  greatly  increased 
virulence.  The  local  outbreaks  of  interepidemic  times  are  not  due  to 
the  virus  which  causes  the  great  pandemics  and  should  be  called 
pseudo-influenza  in  contrast  to  influenza  vera.  Following  the  pande- 
mic it  is  true,  however,  that  for  a  succession  of  years  local  outbreaks 
occur,  due  to  the  pandemic  virus  which  has  been  left  deposited  in  small 
endemic  foci.     These  disappear  in  the  course  of  a  few  years. 

2.  The  second  hypothesis  is  similar  to  the  first,  except  that  in 
it  is  considered  the  possibility  of  there  being  more  than  one  endemic 
focus,  at  least  two,  one  in  the  old  world  and  one  in  the  new.  Although 
Leichtenstern  believed  in  the  first  hypothesis  he  did  not  deny  the 
possibility  of  the  second. 

''There  have  been  in  the  past  several  well  described  influenza 
epidemics  limited  to  North  America.  Furthermore  true  pandemics 
have  occurred  at  the  same  time  in  North  America  and  in  Europe.     We 


AN    EPIDEMIOLOGIC    STUDY  61 

can  suggest  the  hypothesis  that  there  is  a  permanent  endemic  focus, 
just  as  in  central  Asia  and  Russia,  existing  in  the  southern  part  of 
North  America.  The  following  facts  concerning  the  last  pandemic 
periotl  favor  this  idea. 

"As  early  as  May,  1889,  influenza  began  in  Athabasca  (Briti.sh 
North  America)  and  in  the  summer  of  1889,  in  Greenland.  It  is 
especially  interesting  to  hear  of  an  extensive  influenza  epidemic  which 
in  the  middle  or  toward  the  end  of  December,  1889,  broke  out  in  the 
Northwest  Territory  of  British  North  America,  in  Manitoba,  in  the 
Island  of  Vancouver,  similar  to  that  in  the  east  of  Canada  and  Quebec. 
A  spread  of  the  epidemic,  which  attacked  Boston  and  New  York  on 
December  17th,  to  the  above  territories,  far  away  and  connected  by 
very  poor  transportation  facilities,  is  certainly  improbable,  especially 
in  consideration  of  the  time  at  which  the  two  epidemics  occurred. 

"We  are  told  that  the  invasion  and  the  outbreak  of  influenza  in 
these  vast  territories  occurred  at  practically  the  same  time  at  such 
widely  separated  places  as  Fort  MacLeod,  Saskatchewan,  Prince 
Albert  and  other  military  posts,  and  furthermore  in  isolated  Indian 
camps  and  tribes  between  which  there  was  little  or  no  communication. 

"These  facts  also  indicate  that  we  are  considering  primary  endemic 
pandemics  analagous  to  the  one  which  broke  out  in  July,  1889,  in 
Central  Asia." 

3.  The  virus  of  influenza  is  more  or  less  uniformly  distributed 
throughout  the  world.  We  may  say  that  it  is  endemic  in  many 
localities,  as  is  the  case  with  the  meningococcus.  Quite  frequently 
in  one  locality  or  another  the  virus  acquires  increased  virulence  and 
causes  a  small  local  epidemic  which  may  even  spread  to  adjoining 
territories.  It  is  possible  that  the  virus  in  two  or  more  separated 
locahties  may  become  more  invasive  simultaneous!}',  thus  causing 
widely  separated  and  unrelated  outbreaks.  As  a  rule  the  virulence 
does  not  become  so  great  as  to  cause  a  true  pandemic,  but  at  rare 
intervals,  usually  of  decades,  or  thereabouts,  the  epidemic  virus 
becomes  so  greatly  enhanced,  perhaps  from  passage  to  new  territory 
and  through  non-immune  individuals,  that  it  eventually  commences 
on  its  wild  career  around  the  earth.  Perhaps  the  pandemic  variety 
usually  comes  from  one  particular  locality  among  the  many  endemic 
spots.  Perhaps  always  from  the  same  localit}'  or  perhaps  at  times 
even  simultaneously  from  many  different  ones.  It  is  possible  even 
that  an  increased  virulence  develops  simultaneously  in  all  localities. 
This  third  hypothesis  develops  into  a  discussion  as  to  whether  the 
small  interpandemic  epidemics  are  true  influenza  or  some  other  disease. 

6 


62  INFLUENZA 

Again,  Leichtenstern,  although  he  does  not  favor  it,  recognizes  the 
possibihty  of  this  theory : 

"Whether  the  small  local  epidemics  reported  by  Kormann  in 
Coburg  in  1878  and  by  O.  Seifert  in  Wiirzburg  in  1883  are  the  same  as 
the  true  epidemic  influenza  is  at  present  uncertain.  Some  of  the 
complications,  such  as  swelUng  of  the  neck  glands,  and  especially 
frequently  parotitis,  purpura,  scurvy,  indicate  that  the  epidemic  in 
Russia,  in  1856-1858,  reported  by  Kasin,  was  not  the  true  influenza. 

"When  W.  Ziilzer  writes  in  1886  of  an  epidemic  in  Berlin  in  which 
many  thousands  of  individuals  were  attacked,  the  question  might 
arise,  is  this  the  same  influenza  which  three  years  later  passed  through 
the  entire  world  and  which  in  Berlin  was  believed  by  the  same  physici- 
ans to  be  a  new  disease? 

"The  evidence  is  better  in  the  case  of  the  epidemic  reported  by 
von  den  Velden  in  1874-75.  First,  because  of  the  complication  with 
pneumonia  and  especially  because  at  the  same  time  the  disease  sprang 
up  in  several  places  in  France,  South  Germany  and  the  Rhine  Pro- 
vinces. It  is  very  doubtful  whether  epidemics  described  in  1855  and 
1862  in  Iceland,  in  1870  in  Philadelphia,  in  1875  in  Scotland,  in  1876 
in  the  Fiji  Islands,  in  1887  in  several  places  of  England,  in  October, 
1889  in  Natal,  in  November,  1889  in  Jamaica  and  Prince  Edward 
Island,  was  the  true  influenza,  even  though  the  complications  of 
pneumonia  in  the  last  named  epidemics  favor  this  assumption.  As 
regards  the  influenza  epidemic  which  attacked  specially  the  school 
children  of  Pleshey  and  Great- Waltham  and  from  which  fifty  per  cent, 
became  ill  in  November  and  December,  1889,  whereas  the  pandemic 
was  known  to  have  begun  there  in  January,  1890 — the  high  percentage 
of  school  children  that  were  attacked  renders  the  conclusion  that  this 
was  influenza  very  doubtful. 

"It  is  an  entirely  different  matter  concerning  the  last  epidemic 
in  which  the  epidemiologic  compilations,  based  on  retrospective 
diagnoses  suggest  that  in  many  places  of  Germany  the  'first  case'  of 
even  small  epidemic  outbreaks  was  observed  as  early  as  the  summer 
and  autumn  of  1889;  in  other  words,  several  months  before  the  out- 
break of  the  true  pandemic  in  December." 

Leichtenstern  believed  that  the  so-called  catarrhal  fever  and 
epidemics  of  "cold"  which  some  have  been  accustomed  to  call  grip  or 
influenza  are  not  the  true  disease,  although  he  admits  that  there  is  no 
pathognomonic  sign  by  which  the  diseases  may  be  differentiated.  He 
expected  that  search  for  the  influenza  bacillus  which  had  recently 
been  discovered    would    enable    investigators    to  determine  by  its 


AN    EPIDEMIOLOGIC    STUDY  63 

presence  or  absence  whether  or  not  these  local  epidemics  are  true 
influenza. 

This,  of  course,  would  depend  on  the  proof  that  the  influenza 
bacillus  is  the  cause  of  the  disease.  If  the  many  local  influenza  out- 
breaks which  Hirsch  has  collected  in  his  exhaustive  historical  tables 
are  the  same  disease  as  true  influenza,  then  the  picture  of  influenza 
must  be  considered  as  rather  protean.  Leichtenstern  adds  that  this  is 
a  possibility  which  from  present  information  we  cannot  deny.  He 
writes:  "If  such  is  the  case  we  must  give  the  following  epidemiological 
definition  of  influenza:  Influenza  is  a  specific,  infectious  disease  usually 
occurring  epidemically  which,  however,  is  endemic  over  the  entire 
earth,  as  indicated  by  outbreaks  of  cases,  and  which,  after  years  and 
decades  have  passed,  breaks  out  in  epidemic  proportions.  It  is 
recognized  nearly  every  year  in  one  or  another  place  on  the  earth 
where  it  becomes  epidemic.  From  time  to  time  from  some  point  or 
center,  or  from  several  points,  as  for  instance  simultaneously  in  the 
old  and  new  world,  and  for  reasons  unknown  to  us,  an  enormous 
increase  in  virulence  of  the  specific  virus  occurs  and  with  it  a  great 
increase  in  the  contagiousness  of  the  disease.  Those  are  the  times 
when  influenza  spreads  in  mighty  epidemics  over  wide  stretches  of 
land  and  portions  of  the  earth,  or  over  the  whole  earth.  Our  common 
epidemic  influenza  or  grip,  occurring  practically  isolated  or  in  very 
small  outbreaks,  belongs  to  the  same  type  of  disease  as  the  pandemic 
variety,  but  is  due  to  a  mitigated  form  of  the  causative  organism,  one 
of  decreased  virulence  and  of  shorter  viability. 

"Provisionally,  however,  we  will  hold  until  the  proof  has  been 
obtained  by  bacteriological  methods  that  influenza  nostras  and  in- 
fluenza pandemica  are  two  entirely  different  diseases,  just  as  are  chol- 
era nostras  and  asiatica.  Accordingly,  we  will  divide  the  diseases 
designated  as  influenza  in  the  following  way : 

"1.  Influenza  vera,  caused  by  the  Pfeiffer  bacillus. 

"2.  The  endemic-epidemic  influenza  vera  which  arises  from  the 
germ  remaining  after  the  spread  of  the  influenza  pandemic  and  which 
is  caused  by  the  same  germ,  the  bacillus  of  Pfeiffer.  The  duration  of 
this  endemic  state  of  influenza  vera  may  last  years  in  single  localities. 

"3.  The  endemic  influenza  nostras,  or  pseudo-influenza  or  ca- 
tarrhal fever,  commonly  called  grip,  a  disease  sui  generis.  The  germs 
causing  this  disease  are  at  present  as  little  known  as  are  those  of 
cholera  nostras." 

Parkes,  in  1876,  recognized  these  possibilities:  "The  exact  spot 
has  not  been  made  out.     Two  opinions  prevail.     First,  one  focus; 


64  INFLUENZA 

second,  many  foci.  Each  nation,  in  turn,  attributes  the  disease  to  its 
neighbor  and  from  the  names  so  given  one  can  follow  the  direction  of 
the  epidemic."  Noah  Webster  believed  that  in  1698,  1757,  1761  and 
1781  it  originated  first  in  America.  Hirsch  believed  that  some  of 
the  epidemics  had  probably  originated  in  North  America. 

We  find  then  that  after  the  pandemic  of  the  last  century  the  same 
epidemiologic  questions  had  arisen  that  have  come  into  such  promi- 
nence during  the  present  period.  As  a  rule  those  who  have  quoted  the 
epidemiologists  of  1890  to  1900  have  mentioned  the  first  hypothesis 
and  have  failed  to  allude  to  the  fact  that  the  other  two  were  con- 
sidered. So  we  see  that  the  subject  was  by  no  means  settled  even  at 
that  time,  and  that  if  we  should  discover  that  the  1918  pandemic 
cannot  be  traced  to  a  single  endemic  focus  our  results  will  not  be 
absolutely  contradictory  to  those  of  the  last  century. 

Returning  to  a  consideration  of  the  period  1916-1918,  we  observe 
from  reference  to  Frost's  diagram  that  in  the  spring  of  1918  there  was 
a  sharp  and  general  rise  in  mortality  from  influenza  and  pneumonia. 
Frost  reports  that  in  the  larger  cities  on  the  Atlantic  seaboard  this 
increase  occurred  generally  during  January,  February  and  March, 
when  pneumonia  mortality  normally  reaches  its  maximum.  The 
•increase  was  not  so  evident  in  all  these  cities  as  it  was  in  New  York 
City.  In  the  rest  of  the  country,  especially  in  the  Central  and  Western 
States,  the  increase  occurred  in  April,  a  month  during  which  pneu- 
monia mortality  is  generally  on  the  decline,  and  was  sufficient  to 
constitute  an  unmistakable  departure  from  the  normal.  The  increased 
mortality  rate  extended  quite  generally  into  May  and  in  some  areas 
still  longer.  This  is  the  first  increase  after  1916  that  is  pictured  in  the 
mortality  statistics  for  the  country  at  large. 

There  are  some  who  believe  that  they  saw  influenza  in  mild  form 
in  the  United  States  army  in  the  year  1917.  V.  C.  Vaughan  has 
investigated  this  possibility  and  from  a  study  of  the  sick  and  wounded 
charts  decided  that  there  was  no  relation  between  influenza  and  the 
pneumonia  which  was  prevalent  in  1917,  and  which  usually  was 
secondary  to  measles,  being  caused  by  the  streptococcus  in  the  ma- 
jority of  localities.  The  lack  of  association  between  influenza  and 
pneumonia  in  1917  and  the  direct  association  in  1918  is  well  brought 
out  by  a  comparison  of  the  figures  in  the  two  following  charts,  prepared 
by  V.  C.  Vaughan: 


AN    EPIDEMIOLOGIC    STUDY 


63 


Pneumonia  as  a  Sequel  to  Respiratory  Diseases. 
(All  troops  in  United  States  in  1917.) 


Primary  diseases. 


Measles 

Scarlet  Fever 

German  Measles 

Bronchitis 

Influenza 

Meningitis 

Tonsillitis 

Pulmonary  tuberculosis 

Laryngitis 

Diphtheria 

Mumps 

Pharjmgitis 


No.  of  cases 

Per  cent,  of  cases 

No.  of  cases. 

followed  by 

followed  by 

pneumonia. 

pneumonia. 

47,573 

2,075 

4.37 

1,966 

54 

2.75 

8,982 

39 

0.43 

41,233 

20 

0.049 

32,248 

19 

0.059 

1,027 

13 

1.27 

43,021 

7 

0.016 

6,799 

6 

0.088 

4,633 

2 

0.043 

1,163 

1 

0.086 

21,725 

0 

0.000 

8.096 

0 

0.000 

Influenza  and  Pneumonia  in  Last  Four  Months  of  1918. 

Number  of  cases  of  influenza 338,343 

Number  of  cases  of  influenza  followed  by  pneumonia 50.700 

Number  of  deaths  from  influenza  pneumonia 17,700 

Stallybrass,  who  has  studied  the  influenza  and  pneumonia  deaths 
in  Liverpool,  England,  since  the  1889  pandemic,  states  that  in  every 
year  there  had  been  reflected  in  the  curves  evidence  of  periodic 
increase  in  deaths  from  influenza  and  pneumonia,  and  he  states  that 
from  1914  onward  there  has  been  a  progressive  increase  in  the  annual 
number  of  influenzal  deaths  w^ith  the  single  exception  of  1917. 

It  becomes  evident  that  we  cannot  with  the  information  at  hand 
find  any  one  locality  in  which  the  disease  was  prevalent  sufficiently 
ahead  of  the  pandemic  and  to  the  exclusion  of  other  localities,  so 
that  we  might  determine  accurately  the  site  of  origin.  The  next  step 
will  be,  then,  to  discover  as  accurately  as  possible  the  date  at  which 
various  communities  were  first  definitely  attacked  by  the  great 
pandemic,  and  to  search  out  the  localit}'  first  affected. 

Date  of  First  Ixcreased  Prevalexce  ix  VARiors  Localities. 

From  table  II  w^hich  gives  the  earliest  recorded  dates  of  increased 
prevalence  in  different  localities,  we  can  gain  a  fairly  accurate  idea  as 
to  the  direction  and  manner  of  spread  of  the  disease  during  the  pan- 
demic. Influenza  was  first  noticed  in  the  United  States  early  in 
]\Iarch,  1918.  By  the  end  of  the  month  it  had  become  more  dis- 
seminated  in  very  mild  form  over  many  of  the  States  east  of  the 


66 


INFLUENZA 


TABLE  II. 

The  spread  of  influenza  in  1918. 


Month. 

Date. 

Country. 

City. 

Authority  quoted. 

March 

China 

Japanese  Navy 
Japan 

McNalty,  Carnwath. 
McNalty,  Carnwath. 
Jour.  Am.  Med.  Assn. 

France 

Civilian   Population   at 
Chaumont 

MacNeal. 

5 

United  States 

Kansas  _ 

Camp  Funston 

Opie. 

Missouri 

Kansas  City 

V.  C.  Vaughan. 

Illinois 

Chicago 

Frost. 

Ohio 

Columbus 

V.  C.  Vaughan. 

Michigan 

Detroit 

V.  C.  Vaughan. 

18 

Georgia 

Camp  Greenleaf 
Atlanta 

V.  C.  Vaughan. 
V.  C.  Vaughan. 

28 

S.  Carolina 

Camp  Sevier 

W.  T.  Vaughan. 

30 

Kansas 

Haskell 

Pubhc  Health  Reports. 

April 

United  States 

Various   points   from    Nor- 
folk to  Louisiana 

Public  Health  Reports. 

Mississippi 

Camp  Shelby 

V.  C.  Vaughan. 

Georgia 

Camp  Hancock 

Forbes  and  Snyder. 

30 

California 
France 

San  Quentin  Prison 

Stanley. 

Netter. 

Chauffard. 

Messary. 

Longcope. 

1 

Brest     (American    Expedi- 
tionary Forces) 

British  Expeditionary 
Forces 

Allied  Western  Front 

V.  C.  Vaughan. 

Carnwath. 

Public  Health  Reports. 

1 

German  Western  Front 

Gins. 

May 

France 

Chaumont 

Zinsser. 

Scotland 

Glasgow 

Dunlop,  Carnwath. 

Spain 

Madrid 

Office    International 
d' Hygiene  PubUque. 

Greece 

Athens 

Filtzos. 

Macedonia 

French  Army 

Teissoniere,    Beguet    and 
Jolly. 

Egypt 

Egyptian    Expeditionary 
Forces 

Benj  afield. 

Italian  Navp 

MacNeal. 

June 

England 

Portsmouth 

Carnwath. 

15 

Birmingham 

Public  Health  Reports. 

1 

Switzerland 

Zurich 

Office    International 
d'Hygitoe  Publique. 

1 

Germany 

Frankfurt,  A.  M. 

Deutsche,     med.     Wchn- 
schr. 

3 

Strasbourg  (Alsace) 

Rose. 

25 

Bonn 

Koepchen. 

At  the  end 

f  Berlin 

\  North  &  South  Germany 

Deutsche,     med.     Wchn- 

of  the 

schr. 

month 

Late 

Austria 

Vienna 

Bohm. 

15 

Norway 

Christiania 

Pubhc  Health  Reports. 

15 

China{->) 

Chefoo 

Pubhc  Health  Reports. 

16 

Brazil 

Santos 

Pubhc  Health  Reports. 

22 

India 
Porto  Rico 
Philippine    Is- 
lands 

Bombay 

Public  Health  Reports. 

Atiles. 

Hernando 

AN    EPIDEMIOLOGIC    STUDY 


67 


TABLE  II  (Continued). 
The  spread  of  influenza  in  1918. 


Month. 

Date. 

Country. 

City. 

Authority  quoted. 

July 

1 

Germany 
Italy 

Dresden 

Schmorl. 

Office    International 
d'Hygi^ne  Publiquc. 

13 

Sweden 

Malmo 
Gothenburg 

Frost  and  Sydenatricker. 

Late 

Netherlands 

Flushing 

Public  Health  Reports. 

27 

China 

Chungking 

Public  Health  Reports. 

India 

Calcutta 

Malone. 

August 

India 

Punjab 

.Jour.  Am.  Med.  Assn. 

3 

West  Indies 

Guadeloupe 

PubHc  Health  Reports. 

United  States 

Boston 

Second  Spread. 

September 

Denmark 

Frost  and  Sydenstricker. 

11 

Republic   of  Sal- 
vador 

Public  Health  Reports. 

16 

Honduras 

Frost  and   Sydenstricker 

25 

Bermuda 

Frost   and   Sydenstricker. 

30 

Jamaica 

Frost  and   Sydenstricker. 

Mexico 

Santa  Cruz 

Frost   and  Sydenstricker. 

21 

Canada 

Victoriaville 

Quebec 

Hamilton 

Frost  and  Sydenstricker. 

30 

Portugal 

Lisbon 

Public  Health  Reports. 

28 

Morocco 

Tangier 

Frost  and   Sydenstricker. 

14 

South    Africa 
Union 

Frost   and   Sydenstricker. 

16 

Senegal 

Dakar 

Public  Health  Reports. 

16 

Sierra  Leone 
Korea 
United  States 

Freetown 

West      and      South      from 
Boston 

Public  Health  Reports. 
Schofield. 

October 

Early 

Alaska 

Governor's    Annual    Re- 
port. 

1 

Russia 

Archangel 

Frost  and  Sydenstricker. 

Peru 

Lima 

Soldan. 

Uruguay 

Montevideo 

Frost  and   Sydenstricker. 

25 

Venezuda 

Frost  and  Sydenstricker. 

11 

Guatemala 

Frost   and   Sydenstricker. 

12 

Costa  Rica 

Limon 

Frost   and   Sydenstricker. 

26 

Colombia 

Begota,     Barranguilla. 
Cartagena,  Peru. 

Frost  and  Sydenstricker. 
Frost   and   Sydenstricker. 

9 

Cuba 

Camagney,  Nuevita? 

Frost   and   Sydenstricker. 

22 

Azores 

Public  Health  Reports. 

18 

Canary  Islands 

19 

Madagascar 

Frost   and   Sydenstricker. 

17 

Australia 

Frost   and   Sydenstricker. 

19 

New  Zealand 

Frost   and   Sydenstricker. 

Hawaii 

Honolulu 

Frost   and   Sydenstricker. 

November 

British  Guiana 

Rose. 

Dutch  Guiana 

Paramaribo 

Frost  and  Sydenstricker. 

22 

Samoa 

Apia 

Frost  and   Sydenstricker. 

Arabia 

Aden 

Frost  and  Sydenatricker. 

Iceland 

Erlendsson. 

December 

Paraguay 

Paraguay,  Asuncion 

Frost   and   Sydenstricker. 

19 

Dominican       Re- 
public 
Lapland 

La     Plata,     Puerto    Plata, 
Santo  Domingo 

Frost  and  Sydenstricker. 
Macklin. 

8 

Society  Islands 

Frost  and  Sydenstricker. 

3 

Tonga  Islands 
Fiji  Islands 

Frost  and  Sydenstricker. 
Frost  and   Sydenstricker. 

68  -  INFLUENZA 

Mississippi  and  a  few  West  of  that  line.  The  following  month  the 
disease  appeared  in  France.  In  the  American  Expeditionary  Forces 
in  France  it  first  appeared  at  the  base  ports  which  were  receiving 
troops  from  the  United  States.  During  this  month  the  disease  had 
reached  the  alHed  Western  front,  the  German  front  had  become 
infected  and  probably  the  disease  had  started  on  its  travel  inward  into 
enemy  country.  In  May  the  disease  was  reported  present  in  Scotland, 
Spain,  Greece  and  Egypt.  In  June  England  became  infected,  as  also 
Switzerland,  Germany,  Austria  and  Norway.  In  this  month  the 
disease  had  reached  as  far  as  South  America  and  India.  In  China,  on 
the  15th  of  June,  there  was  reported  an  epidemic  of  a  disease  resembl- 
ing dengue  which  affected  fifty  per  cent,  of  the  population  in  Chefoo 
and  Shanghai.  This  disease  may  well  have  been  influenza.  During 
July  the  disease  had  spread  through  Germany,  appearing  according  to 
German  reports  in  the  cities  toward  the  West  earlier  than  in  BerHn 
and  other  more  Eastern  cities,  including  Vienna.  In  July  the  disease 
was  present  in  other  countries  of  Europe  and  was  again  reported  in 
China  and  India. 

During  its  course  through  Europe  influenza  had  developed  a 
greatly  heightened  virulence  and  toward  the  end  of  August  it  again 
appeared  in  the  United  States  apparently  travehng  in  a  reverse 
direction  from  that  of  its  first  spread  and,  entering  the  country  at 
Boston,  it  spread  to  the  West  and  South  until  the  entire  country 
was  covered.  The  West  Indies  were  invaded  early  in  August  and  in 
the  same  month  the  disease  had  spread  through  India  as  far  as  the 
Punjab.  In  September  the  epidemic  continued  through  the  West 
Indies  attacked  Mexico  and  Canada,  and  had  attained  such  remote 
locaUties  as  the  South  Africa  Union,  Senegal  and  Korea.  In  October 
the  spread  was  particularly  distributed  through  South  America,  and 
in  this  month  again  remote  localities  such  as  Alaska,  New  Zealand, 
the  Hawaiian  Islands,  AustraHa,  and  Madagascar  were  reached. 
Islands,  which  although  not  very  remote,  were  isolated  except  for  the 
arrival  of  occasional  ships,  such  as  Cuba,  the  Azores  and  the  Canary 
Islands,  were  first  reported  attacked  in  October.  In  November  the 
spread  continued  throughout  the  world,  and  among  the  more  remote 
locahties  should  be  mentioned  Samoa,  Arabia,  Iceland.  In  December, 
Lapland,  the  Society  Islands  and  the  Fiji  Islands  were  invaded  (see 
Chart  XI). 

It  is  particularly  of  interest  to  follow  the  spread  of  the  disease 
in  Europe.  Perhaps  the  chief  characteristic  is  the  distribution  equally 
to  the  north  and  south  of  France,  a  country  which  appears  to  have 


CHART  XI. 


Anarch 


•7   ^^ 


A/Dr/7 


K^^^^> 


Mc7y      if 


^  j^' 


f^. 


s^^' 


?  y^ 


•^ 


z' 1 


•c    ^y 


^e/>/eMi>6 


/\  ugu^f'^i 


l7cfo/D 


jw-/""^^^^-  -v,^     <?a>(? 


Cinematogram  showing  the  spread  of  influenza  in  1918  from  a  presumptive  primaiyfocus 
in  the  United  States. 


A\    EPIDEMIOLOGIC    STUDY'  09 

been  invaded  early.  In  May  it  spread  to  Scotland  and  to  Spain, 
Greece  and  Egypt.  In  June  the  spread  was  in  three  directions,  to 
England  and  Norway  on  the  North,  to  Switzerland,  Germany  and 
Austria  on  the  East,  and  again  into  Spain  and  Italy  on  the  South. 

The  correctness  of  the  foregoing  description  of  the  spread  of 
influenza  depends  first,  upon  the  accuracy  of  the  authorities  quoted, 
and  particularly  upon  our  having  discovered  the  earliest  report  for 
each  countr3\  The  author  believes  that  the  information  as  obtained 
for  the  United  States  represents  nearly  the  true  state  of  afifairs,  and 
that  the  error  present  is  negligible.  The  information  obtained  for 
France  is  based  upon  the  statements  of  excellent  investigators,  Netter, 
Chauffard  and  Massary,  for  the  French  population,  and  MacNeal, 
Zinsser  and  Longcope,  for  the  American  Expeditionary  Forces.  Here 
the  statements  agree  both  for  the  military  and  for  the  civil  population 
that  there  was  no  widespread  influenza  in  France  much  before  April 
1st.  Also,  the  author  feels  that  the  information  for  England  and 
Scotland  is  authoritative  and  will  not  later  be  changed.  It  is  based 
particularly  upon  the  excellent  reports  by  Carnwath,  who  has  investi- 
gated the  subject  in  great  detail.  The  excerpts  from  the  German 
literature,  although  not  abundant,  are  practically  unanimous  in 
agreeing  as  to  the  date  of  invasion  in  Germany.  The  reports  from 
the  remaining  countries  of  Europe  have  been  less  abundant,  and 
frequently  the  author  has  been  forced  to  rely  upon  a  report  by  only 
one  individual;  but  while  the  date  may  be  in  error,  yet  the  month  of 
occurrence  is  probably  correct. 

For  other  continents,  Asia,  Africa  and  South  America,  the  reports 
as  far  as  they  go  appear  reliable,  but  it  is  impossible  to  prove  that  at  an 
earlier  date  there  was  not  a  very  mild  epidemic  in  some  one  of  these 
locaHties,  similar  to  the  earlier  epidemic  in  the  United  States,  which 
escaped  detection.  It  is  particularly  important,  in  view  of  the  1889 
experience,  that  we  obtain  if  possible  fuller  information  on  the  earliest 
time  of  the  appearance  of  the  disease  in  China  and  other  parts  of 
Asia,  and  that  we  determine  whether  there  was  a  spread  from  that 
continent  to  America  previous  to  March,  1918. 

Several  factors  have  added  considerably  to  the  difficulty  in  tracing 
the  site  of  origin  of  the  1918  epidemic  and  its  direction  of  spread.  The 
principal  of  these  have  been  the  speed  of  modern  travel,  the  character 
of  modern  commerce,  and  the  existence  of  a  state  of  war.  The 
channels  of  the  commerce  of  today  radiate  nearly  from  all  points  to  all 
other  points  of  the  civihzed  world.  No  longer  are  there  a  few  pre- 
eminent lanes  of  travel,  such  as  there  were  in  1580  when  the  epidemic 


70  INFLUENZA 

spread  clearly  from  Constantinople  to  Venice  and  on  to  Hungary  and 
Germany,  finally  finding  its  way  to  Norway,  Sweden,  Denmark  and 
Russia.  The  war  has  made  it  difficult  to  know  accurately  the  date 
and  direction  of  spread  in  enemy  countries.  We  have  practically  no 
information,  except  that  in  the  public  press,  from  Russia  and  the  Bal- 
kan States.  By  October  of  1918  the  severe  form  of  the  disease  had 
become  prevalent  in  every  continent,  and  by  December  it  had  reached 
the  farthest  islands  of  the  Southern  Pacific  ocean. 

The  apparent  difference  in  the  direction  of  spread  between  1889  and 
1918  makes  comparison  of  rapidity  difficult.  But  if  we  take  as  our 
starting  point  the  time  at  which  each  epidemic  became  prevalent  in 
commercial  centers  of  Europe  and  the  time  at  which  it  finally  reached 
localities  well  off  the  usual  paths  of  commerce  we  will  see  that  there  is 
some  difference,  the  disease  spreading  more  rapidly  in  the  recent 
epidemic,  but  that  the  difference  is  no  greater  than  could  be  accounted 
for  by  the  more  modern  means  of  communication.  From  April,  1918, 
when  the  disease  appeared  in  France,  to  October,  when  it  was  reported 
in  Madagascar,  is  six  months.  From  October,  1889,  with  the  disease 
prevailing  in  Petrograd,  to  July,  1890,  when  it  appeared  in  Madagas- 
car, is  nine  months.  It  required  seven  months  after  the  disease 
became  epidemic  in  France  this  time  for  it  to  appear  in  Iceland,  and 
nine  months  in  1889-90. 

The  earliest  recorded  epidemic  of  influenza  in  the  United  States  in 
the  spring  of  1918  (but  which  was  not  recognized  to  be  such  until 
later)  appears  to  have  been  that  at  Camp  Funsten,  described  by 
Opie  and  his  associates  as  having  appeared  in  that  Camp  March  5th. 
The  epidemic  swept  quickly  throughout  the  Camp  and  spent  itself 
as  rapidly.  A  second  wave  appeared  in  April  and  in  May  a  third,  both 
of  which  were  almost  entirely  limited  to  newly  drafted  men  brought  into 
camp  subsequent  to  the  preceding  outbreaks.  Correlated  with  each 
of  these  three  outbreaks  was  a  period  of  increased  incidence  of  pneu- 
monia and  bronchitis,  frequently  occurring  in  influenza  cases.  These 
complicating  diseases  were  prevalent  in  the  organizations  attacked  by 
the  influenza  and  maintained  the  same  relation  to  the  length  of  service 
of  the  men  affected.  ' 

The  next  report  of  influenza  in  the  United  States  was  from  the 
Oglethorpe  camps,  beginning  about  March,  18,  1918.  Within  two 
weeks  every  organization  in  Camp  Forrest  and  the  Reserve  Officers 
Training  Camp  was  affected.  After  about  three  weeks  the  epidemic 
subsided  rapidly.  Fourteen  hundred  and  sixty-eight  cases  were  sent 
to  the  hospital  out  of  a  total  strength  of  28,586.     It  is  estimated  that 


AN    EPIDEMIOLOGIC    STUDY  71 

2,900   cases   iiad   occurred.     The   clinical   symptomatology   and   the 
epidemic  characteristics  were  described  in  detail. 

On  March  28th  the  author  had  occasion  to  observe  a  similar 
epidemic  at  Camp  Sevier,  South  Carolina,  which  appears  to  have 
attacked  a  smaller  proportion  of  the  troops  in  camp,  but  which  showed 
the  same  epidemiologic  picture.  A  note  in  the  Public  Health  Reports 
states  that  on  March  30,  1918,  the  occurrence  of  eighteen  cases  of 
influenza,  of  severe  type,  from  which  three  deaths  resulted,  was 
reported  at  Haskell,  Kansas.  This  is  the  earliest  report  we  have  been 
able  to  find  concerning  the  disease  in  civil  communities.  That  for 
Chicago  was  practically  contemporary.  The  Commissioner  of  Health 
of  Chicago  states  in  his  special  report  on  the  autumn  epidemic,  that  in 
March,  1918,  distinct  epidemics  resembhng  influenza  were  observed 
in  certain  portions  of  that  city. 

According  to  Public  Health  Reports,  fevers  of  an  undetermined 
nature  were  reported  during  April  and  May  at  various  points  from 
Norfolk  to  Louisiana.  "  An  examination  of  the  records  and  reports  of 
the  physicians  who  had  treated  these  cases  leads  to  the  belief  that  these 
fevers  were  mainly  influenza  of  mild  type."  It  is  possible,  however, 
that  all  cases  reported  were  not  of  the  same  disease,  and  in  one  locality 
in  Louisiana  dengue  may  have  occurred. 

Fleisher  states  that  during  the  latter  part  of  March  and  early 
part  of  April,  1918,  there  occurred  at  Camp  Wadsworth  an  epidemic  of 
measles  and  practically  concomitant  with  it  an  epidemic  form  of 
bronchopneumonia  associated  with  empyema.  During  this  time 
there  were  some  200  cases  of  measles  and  twenty-one  cases  of  broncho- 
pneumonia or  empyema  in  which  a  hemolytic  streptococcus  was  the 
causative  agent.  He  makes  no  mention  of  any  epidemic  of  influenza 
either  in  mild  or  severe  form,  occurring  at  this  period. 

Forbes  and  Snyder  reported  that  during  the  month  of  April,  1918, 
a  highly  contagious,  but  comparatively  mild  infection  of  the  respira- 
tory tract  was  epidemic  in  Camp  Hancock.  Several  thousand  men 
in  the  command  were  infected,  but  relatively  few  were  ill  enough  to 
be  sent  to  the  hospital.  The  only  fatal  case  occurred  early  in  the 
epidemic,  and  it  was  the  observations  made  in  this  case  which  prompted 
the  study  made  by  Forbes  and  Snyder. 

The  fatal  case  had  the  subjective  symptoms  familiar  to  influenza. 
The  physical  findings  were  similar  to  those  occurring  in  influenza  in  the 
later  epidemics.  The  leucocyte  count  was  4,300.  A  blood  culture 
showed  in  twenty-four  hours  a  heavy  growth  of  small  non-motile, 
gram-negative    baciUi    which  the  authors  concluded  to  be  Bacillus 


72  INFLUENZA 

influenzae.  The  leucocyte  counts  made  at  five  hour  intervals  on  a 
later  date  were  respectively,  3,400,  2,200  and  2,300.  A  second  blood 
culture  taken  on  April  10th,  a  day  later,  also  showed  a  pure  culture  of 
the  same  organism.  The  leucocyte  count  had  risen  to  5,600.  At 
necropsy  a  confluent  bronchopneumonia  was  found.  There  was  no 
pleural  effusion  and  the  other  viscera  showed  nothing  remarkable. 
Bacillus  influenzae  was  recovered  from  cultures  taken  from  the  lung 
and  spleen. 

Throughout  this  epidemic  the  chnical  picture  of  the  disease  was 
characteristic.  Nearly  every  patient  gave  as  the  initial  symptoms 
backache,  headache,  sHght  cough  or  sore  throat.  Conjunctivitis  and 
a  marked  injection  of  the  soft  palate  were  noted  in  ninety  per  cent,  of 
the  cases.  In  addition,  a  sHght  or  moderate  general  adenopathy  was 
often  observed.  The  face  was  flushed  and  in  a  few  cases  the  skin  of 
the  thorax  presented  a  mild  erythema.  In  three  cases  a  provisional 
diagnosis  of  scarlet  fever  was  made  until  the  blood  count  showed  a 
leucopenia.     Leucopenia  was  characteristic  of  all  cases. 

During  the  early  April  epidemic  at  this  camp,  nasopharyngeal 
cultures  showed  an  organism  resembling  Bacillus  influenzae  in  seven- 
teen out  of  thirty-three  cases,  but  the  identity  of  the  organism  was  not 
established  by  subcultures.  In  ten  cases  in  which  sputum  examin- 
ations were  made,  Bacillus  influenzae  was  found  in  only  four;  strepto- 
cocci were  present  in  six.  Blood  cultures  on  twenty  consecutive 
non-fatal  cases,  only  one  of  which  was  complicated  by  broncho- 
pneumonia, were  all  negative. 

V.  C.  Vaughan  reports  that  at  Camp  Shelby,  Hattiesburg,  Miss., 
there  was  in  April  a  division  of  troops  numbering  about  26,000.  An 
epidemic  of  mild  influenza  struck  this  camp  in  April,  1918,  and  within 
ten  days  there  were  about  2,000  cases.  This  included  not  only  those 
who  were  sent  to  the  hospitals,  but  also  those  who  were  cared  for  in 
barracks.  This  was  the  only  division  that  remained  in  this  country 
without  change  of  station  from  April  until  the  fall  of  1918.  During 
the  summer  this  camp  received  20,000  recruits.  In  October,  1918, 
the  virulent  form  of  influenza  reached  this  camp.  It  confined  itself 
almost  exclusively  to  the  recruits  of  the  summer,  and  scarcely  touched 
the  men  who  had  hved  through  the  epidemic  of  April.  Not  only  the 
2,000  who  had  the  disease  in  April,  but  the  24,000  who  apparently 
were  not  affected,  escaped  the  fall  epidemic. 

Vaughan  also  remarks  that  in  March  and  April  of  1918  there  was  an 
unusually  high  death  rate  from  pneumonia  in  Atlanta,  Ga.,  Kansas 
City,  Mo.,  Detroit,  Mich.,  and  Columbus,  Ohio,  while  in  the  autumn 


AN    EPIDEMIOLOGIC    STUDY  73 

epidemic  these  cities  suffered  rather  less  than  the  average.  In  view  of 
the  experience  at  Camp  Shelby  he  reasons  that  there  was  probably 
mild  influenza  in  these  cities  in  March  and  April  of  1918.  It  may  he 
stated  that  in  the  mortality  statistics  for  1918,  the  abnormally  high 
death  rates  for  respiratory  diseases  during  March  and  April  were 
present  throughout  the  registration  area  of  the  United  States. 

The  first  reports  that  we  have  been  able  to  discover  concerning 
influenza  on  the  Pacific  Coast  are  for  the  month  of  April.  Stanley 
reports  three  successive  waves  of  epidemic  influenza  at  San  Qucntin 
Prison,  Cal.  The  first  began  on  April  30,  1918,  with  the  entrance  into 
the  institution  of  a  prisoner  who  was  sick  on  admission. 

Following  the  disease  in  its  possible  spread  to  the  next  continent  we 
are  inclined  to  conclude  that  it  was  carried  to  France  with  the  great 
body  of  men  traveling  to  that  country  from  the  United  States.  Mac- 
Neal  and  Longcope  both  report  that  in  the  first  outbreak  in  the  Ameri- 
can Expeditionary  Forces  the  earhest  recorded  epidemic  appeared 
about  April  1,  1918,  in  a  rest  camp  near  Bordeaux.  It  reached  its 
height  April  22d  and  ceased  May  5th.  According  to  V.  C.  Vaughan 
a  mild  epidemic  of  influenza  and  pneumonia  prevailed  at  Brest  and 
in  that  vicinity  from  April  1st  to  July  31st,  1918.  During  this  time 
fifty  cases  of  influenza,  twentj'-six  of  which  developed  pneumonia, 
with  two  deaths  were  admitted  to  the  United  States  Naval  Base 
Hospital  at  Brest.  The  disease  was  prevalent  at  the  same  time 
among  the  French  civil,  miUtary  and  naval  groups  in  the  same  locality. 
We  see  then  that  in  the  American  Expeditionary  Forces  at  any  rate 
the  disease  first  occurred  in  two  base  ports  receiving  troops  from  the 
United  States.  In  May,  1918,  a  second  outbreak  was  reported  from 
Tours,  which  lasted  from  May  1st  to  May  24th  and  affected  117 
persons.  Zinsser  reports  an  epidemic  at  Chaumont  during  May  and 
from  this  time  until  July  more  or  less  extensive  epidemics  occurred 
throughout  the  entire  American  Expeditionary  Forces. 

Longcope  remarks  that  the  disease  was  likewise  prevalent  at  this 
time  among  the  French  population  and  in  parts  of  the  British  Army. 
The  Influenza  Committee  of  the  British  Advisory  Board  determined 
that  in  the  first  British  Army  the  disease  became  prevalent  around 
May  18th.  Carnwath  states  that  in  the  British  Army  in  France  the 
epidemic  began  by  a  few  local  outbreaks  in  the  first  and  second  Armies 
in  April  and  May,  1918.  Later  it  spread  to  the  first,  third  and  fourth 
Armies  and  affected  a  very  large  proportion  of  the  troops. 

Small  describes  two  epidemics  of  influenza  in  one  of  the  largest 
General  Hospitals  of  the  British  Expeditionary  Force  in  France.  He 
says  that  the  first  w^ave  began  in  April,  1918. 


74  INFLUENZA 

The  fact  that  MacNeal,  as  we  have  previously  recorded,  beUeved 
that  there  was  influenza  in  France  in  1917,  must  not  be  overlooked. 
Those  earlier  cases  were  scattered  and  did  not  so  far  as  we  know  occur 
in  the  form  of  small  epidemics.  Even  if  these  were  true  influenza  it  is 
reasonable  to  assume  that  they  were  sporadic  cases  and  were  not 
genetically  associated  with  the  epidemic  spreading  from  America  and 
daily  increasing  in  virulence,  which  we  are  now  following.  MacNeal 
concludes  that  epidemic  influenza  in  France  originated  from  the 
endemic  foci  existing  there,  and  that  the  disease  was  probably  carried 
from  Europe  to  the  United  States  by  shipping.  The  author's  opinion 
regarding  the  first  direction  of  spread  is  that  the  reverse  condition  was 
the  actual  process.     Zinsser  likewise  holds  the  latter  view. 

A  most  important  observation  made  by  MacNeal  is  that  French 
physicians  practicing  among  the  civilian  population  were  perfectly 
familiar  with  the  disease  when  it  appeared  at  Chaumont  in  April,  1918, 
that  they  designated  it  as  La  Grippe,  and  stated  that  it  had  been 
extensively  prevalent  in  the  civilian  population  of  Chaumont  from 
March  15th  to  May  15th,  1918.  These  observations  of  influenza 
occurring  in  France  at  almost  the  same  date  as  the  first  outbreaks  in 
the  United  States  is  a  matter  of  great  interest.  It  has  also  been 
stated  by  McNalty  and  by  Carnwath,  who  quotes  Kabeshima  and  Lee, 
that  the  disease  was  prevalent  in  epidemic  form  in  China  and  Japan 
in  March,  1918.  We  have  here  three  foci  from  which  the  disease 
may  have  primarily  originated.  There  are  two  possibilities;  first, 
that  it  originated  in  all  three  foci  (and  perhaps  others) ,  and  spread  to 
all  parts  of  the  world  from  each;  second,  that  the  virus,  distributed 
throughout  the  world,  acquired  high  virulence  in  all  three  localities, 
causing  small  epidemic  outbreaks,  but  that  the  virus  from  only  one 
of  these  places  finally  became  so  exalted  as  to  cause  the  pandemic. 
Did  the  'pandemic  disease  originate  simultaneously  in  France,  in 
China  and  in  the  United  States?  One  fact  seems  certain,  that  the 
influenza  which  attacked  our  troops  in  Europe  was  influenza  imported 
fjom  the  United  States.  We  have  seen  that  it  first  appeared  in  the 
American  Expeditionary  forces  at  the  base  ports.  Alberto  Lutraria, 
Health  Commissioner  of  Italy,  has  reported  that  the  disease  was 
brought  to  that  country  from  America.  A  point  of  significance  is  the 
fact  that  during  March  and  April  there  was  an  unusually  large  troop 
movement  from  the  United  States  to  the  American  Expeditionary 
Forces. 

MacNeal  says:  "The  suggestion  that  the  epidemic  was  introduced 
from  America  is  supported  by  the  fact  that  it  appeared  at  a  time 


A.V    EPIDEMIOLOGIC    STUDY  75 

when  large  numbers  of  Americans  were  arriving  in  Europe,  which  is 
indeed  an  outstanding  feature  correlated  in  time  with  the  onset  of  the 
epidemic." 

According  to  the  report  of  the  Influenza  Committee,  the  disease 
was  first  seen  in  epidemic  form  in  April  and  May  in  the  British  Armies 
in  France,  but  that  was  not  the  first  time  that  Pfeififer's  bacillus  had 
appeared  within  the  armies.  It  had  frequently  been  found  in  cases  of 
bronchopneumonia,  especially  during  the  winter  of  1916-17.  Carn- 
wath  remarks  that  it  is  doubtful  whether  much  importance  from  an 
epidemiologic  point  of  view  attaches  to  these  sporadic  findings  of 
the  influenza  bacillus.  In  an  outbreak  of  measles  and  rubella — 
complicated  by  purulent  bronchitis — which  attacked  men  belonging 
to  the  draft  of  troops  from  New  Zealand  between  Januar}^  1st  and 
March  8th,  1918,  the  bacillus  influenzae  was  present  in  twenty-four 
of  the  forty  sputa  examined,  and  was  grown  in  culture  in  twenty-one 
cases.  Sellards  made  somewhat  similar  observations  on  measles 
patients  at  Camp  Devens. 

Concerning  the  French  population,  Chauffard,  Messary  and 
Netter,  all  remark  that  the  first  cases  in  France  developed  in  April 
with  possibly  some  cases  before  that  time,  and  that  there  were  un- 
doubtedly cases  in  the  German  Army  in  April. 

We  see  then  that  by  April  the  disease  has  been  transferred  to 
France  and  is  prevalent  in  the  various  armies.  It  is  natural  to  assume 
that  the  battle  front  would  present  no  great  obstacle  to  the  spread 
of  the  disease  into  the  German  Army.  Gins  remarks  that  the  disease 
was  present  on  the  German  West  front  among  the  troops  as  early  as 
April,  1918,  and  that  it  spread  from  there  more  rapidly  to  the  South 
than  to  the  North. 

During  the  month  of  Ma}^  we  observe  the  spread  of  the  disease  to 
Great  Britain,  where  Carnwath,  who  has  made  an  exhaustive  study  of 
the  spread  in  Great  Britain,  believes  that  it  was  imported  by  the 
troops  from  France.  Its  first  recorded  appearance  in  Glasgow  was  in 
May.  Dunlop,  in  reporting  the  successive  epidemics  in  Scotland, 
observed  that  in  addition  to  the  three  well  marked  epidemics  there 
was  a  mild  one  recognizable  in  Glasgow  in  ]May,  and  that  in  that  city 
the  death  rate  rose  from  14.1  to  20.1,  and  the  weekly  number  of 
deaths  from  pneumonia  and  bronchitis  from  36  to  107. 

In  England  the  disease  first  attracted  attention  in  June,  appearing 
first  in  the  coast  towns,  chiefly  at  the  beginning  among  the  military 
and  naval  forces.  The  civilian  population  was  severely  affected  only 
later.     The    ports   which   were   earlier   attacked    were   Portsmouth, 


76  -  INFLUENZA 

Southampton  and  Liverpool.  Inland  towns  suffered  more  severely 
later. 

In  the  same  month  that  the  disease  broke  out  in  Scotland  it 
appeared  in  Spain.  The  Inspector  General  of  Health  in  that  country 
reported  that  an  epidemic  of  the  disease  began  at  Madrid  in  the  last 
half  of  May,  1918,  at  a  period  when  there  was  an  unusually  large 
gathering  of  people  in  the  city.  Within  a  short  time  it  had  spread 
rapidly  through  all  the  provinces.  The  increase  in  death  rate  became 
marked  on  the  27th  of  May  and  reached  its  peak  on  the  31st,  at  which 
time  the  rate  was  twice  that  of  the  average  annual  death  rate  for  that 
period  of  the  year.  During  the  following  week  there  was  some 
oscillation  around  the  peak  and  then  the  curve  fell  away.  The 
epidemic  was  particularly  severe  at  Madrid,  Badajoz,  and  Seville. 
It  was  mild  at  Barcelona. 

MacNeal  remarks:  "In  Spain  the  disease  appeared  in  epidemic 
form  about  the  middle  of  May  and  this  outbreak  received  great 
publicity,  sufficient  to  lead  to  the  popular  appellation  of  Spanish 
inffuenza.  The  very  rapid  and  extensive  spread  of  the  disease  in 
Spain  would  indicate  that  it  had  been  introduced  from  without  rather 
than  transformed  from  the-  endemic  state  in  that  country.  This  also 
appears  to  accord  with  the  view  of  those  who  have  studied  the  epidemic 
in  Spain." 

Filtzos  reports  that  influenza  first  appeared  in  Greece  toward  the 
end  of  May,  1918.  The  symptoms  were  slight  and  the  people  who 
were  attacked  suffered  for  three  or  four  days  with  fever,  accompanied 
by  nervous  symptoms.  It  was  called  at  the  time  "Spanish  Fever". 
Beginning  with  September  the  epidemic  became  worse  and  caused  a 
considerable  rise  in  mortality.  Complications  with  bronchopneu- 
monia appeared.  The  decrease  in  incidence  began  toward  the  middle 
of  December,  1918. 

According  to  Benjafield,  the  pandemic  first  commenced  in  the 
Egyptian  Expeditionary  Force  in  May,  1918,  but  the  maximum  inci- 
dence was  not  reached  until  September  and  October.  The  cases 
during  the  earlier  period  of  the  epidemic  were  on  the  whole  mild  in 
type  and  of  short  duration,  only  a  very  small  proportion  being  com- 
plicated by  bronchopneumonia.  The  epidemic  continued  from 
November,  through  February,  1919,  but  the  number  of  cases  showed  a 
marked  decrease  during  the  last  two  months. 

The  month  of  June  saw  the  spread  into  England  which  we  have 
already  described,  and  the  continuation  from  the  German  West  front 
back  into  the  enemy  territory. 


AN    EPIDEMIOLOGIC    STUDY  77 

Rose  reports  that  on  the  3d  of  Juno,  1918,  in  Strasbourg  the  first 
cases  of  influenza  were  reported  in  his  hospital  and  that  by  the  15th 
of  the  month  the  disease  was  practically  epidemic.  Wachter  in 
reporting  cases  from  Frankfurt  a.  M.  says  that  the  cases  of  influenza 
in  that  city  appeared  from  the  beginning  of  June,  1918.  wSchmorl 
remarks  that  influenza  became  epidemic  in  Dresden  in  the  beginning 
of  July,  1918.  According  to  Koepchen,  the  disease  was  epidemic  in 
Bonn  the  25th  of  June. 

An  editorial  comment  in  the  Deutsche  medizinische  Wochenschrift, 
July  4,  1918,  remarks  that  the  influenza  pandemic  "which  probably 
has  spread  from  Spain  in  the  last  few  days"  has  appeared  in  several 
places  in  Germany  in  the  South  and  the  North,  and  in  Berhn.  Accord- 
ing to  the  information  received  up  to  that  time  the  disease  was  of 
short  duration  and  without  severe  complications.  The  issue  of  July 
11th  reports  that  the  influenza  epidemic  appears  to  have  already 
passed  its  peak  in  Berlin  and  that  in  Siiddeutschland  the  spread  of  the 
epidemic  has  become  very  wide. 

The  Office  International  d'Hygiene  Publique  records  that  the 
pandemic  spread  throughout  Switzerland  towards  the  end  of  June, 
1918,  after  having  invaded  a  certain  number  of  European  states, 
coming  from  various  army  fronts.     It  was  at  first  of  mild  severity. 

Bohm  states  that  the  deaths  from  pneumonia  and  influenza  in 
Vienna  began  to  show  an  increase  in  the  week  ending  July  30th.  In 
August  they  returned  to  the  normal  rate.  The  second  wave  occurred 
in  Vienna  in  the  middle  of  September. 

From  the  information  at  our  disposal  we  are  unable  to  determine 
from  what  direction  the  pandemic  entered  either  Switzerland  or 
Austria.  The  point  of  entry  into  Switzerland  is  of  relatively  little 
importance  in  tracing  the  spread  on  the  continent  of  Europe.  Pre- 
sumably it  entered  from  the  north  or  northwest.  The  disease  appeared 
in  Berne  in  June,  reaching  its  height  in  that  canton  in  the  middle  of 
July  and  dying  out  in  August  (Sobernheim  and  Novkaovie). 

Information  of  the  place  of  entrance  into  Spain  is  also  rather 
indefinite.  We  are  told  that  Barcelona  was  one  of  the  cities  attacked 
early.  Barcelona  is  situated  on  the  iVIediterranean  near  the  French 
border  and  is  quite  directly  connected  by  commerce  with  Marseilles 
and  other  French  ports  on  the  Mediterranean. 

In  June  the  disease  had  also  spread  to  Norway  and  outside  of 
Europe  to  the  West  Indies,  South  America,  India  and  China.  A  short 
notice  in  the  Public  Health  Reports  tells  us  that  epidemic  influenza 
with  an  estimated  number  of  1,500  cases  began  in  Christiania,  Norway, 
about  June  15th. 


78  INFLUENZA 

Atiles  relates  that  influenza  appeared  in  Porto  Rico  in  June,  soon 
after  the  arrival  of  a  ship  from  Spain.  It  spread  rapidly,  and  it  is 
estimated  that  at  one  time  fully  eight  per  cent,  of  the  entire  population 
had  the  disease  simultaneously,  and  that  forty  per  cent-  of  the  popula- 
tion were  affected  during  the  epidemic. 

The  Health  Officer  at  Bombay  made  report  in  July,  1918,  on  an 
influenza-hke  disease  then  spreading  throughout  India.  It  was  stated 
that  the  disease  was  introduced  into  Bombay  from  overseas  by  a  trans- 
port which  arrived  May  31,  1918;  that  by  June  22d  the  disease  had 
become  epidemic  at  Bombay,  and  that  it  was  present  in  July,  1918, 
at  Calcutta  and  Madras. 

.  The  rapid  spread  from  Europe  to  distant  India  may  be  accounted 
for  with  the  same  mechanism  as  that  by  which  the  disease  was  spread 
from  America  to  France  and  from  France  to  England,  viz.  by  army 
transports.  The  occurrence  of  the  disease  in  Porto  Rico  appears  to 
have  been  definitely  connected  with  the  arrival  of  a  ship  from  Spain. 
A  very  short  notice  in  the  Public  Health  Reports  tells  us  that  influ- 
enza was  reported  present  at  Santos,  Brazil,  June  16,  1918.  We  are 
not  informed  as  to  how  it  reached  that  place. 

We  have  discovered  no  mention  of  influenza  in  China  in  June.  It 
was  reported  present  in  Chungking,  China,  July  27th.  and  at  that 
time  one-half  of  the  population  was  stated  to  be  affected.  Dengue 
was  reported  prevalent  at  Chefoo,  China,  during  the  two  weeks  ended 
June  15,  1918,  and  a  report  from  Shanghai  of  the  same  date  describes 
the  prevalence  of  a  disease  resembling  dengue  and  affecting  about  50 
'per  cent,  of  the  population.  The  disease  in  these  two  latter  places 
may  have  been  influenza. 

The  epidemic  made  its  appearance  in  Korea  in  September,  1918. 
Schofield  and  Cynn,  who  report  the  epidemic,  believe  that  the  infec- 
tion came  from  Europe  via  Siberia.  The  disease  spread  from  North 
to  South  along  the  line  of  the  Southern  Manchurian  Railway. 

In  August  the  disease  was  re-introduced  into  the  United  States 
and  by  the  end  of  that  month  it  had  acquired  a  foothold  in  Boston 
and  vicinity  and  rapidly  spread  to  other  parts  of  the  country.  The 
pandemic  had  crossed  the  Atlantic  in  both  directions  in  six  months' 
time. 

In  1918  as  in  1889  there  are  excellent  descriptions  of  the  convey- 
ance of  the  disease  by  vessels.  The  transfer  from  Spain  to  Porto 
Rico  has  been  mentioned.  Escomel  says  that  the  outbreak  in  Rio  de 
Janeiro  was  ascribed  to  infection  from  a  steamship  from  Spain,  the 
same  boat  which  later  visited  Buenos  Ayres  and  started  the  epidemic 
m  the  latter  city.  , 


AN    KPIDEMIOLOUIC    STUDY  79 

According;  to  a  report  to  tho  Journal  of  tho  American  Medical 
Association  from  Mexico  the  epidemic  invaded  that  country  from  the 
North  at  Laredo  and  followed  the  course  from  North  to  South.  P'rom 
a  similar  source  the  same  Journal  reports  that  the  influ(;nza  spread 
from  Buenos  Ayres  as  a  primary  focus  to  Paraguay  and  there  acquired 
greater  virulence. 

Hernando  reports  from  the  Philippine  Islands  that  influenza  was 
estimated  to  have  attacked  forty  per  cent,  of  the  total  population  of 
7,000,000  the  mortality  being  about  2.5  per  cent,  of  those  attacked. 
The  epidemic  really  began  in  June,  although  it  did  not  assume  great 
severity  until  October.  The  group  of  ages  that  suffered  most  were 
those  between  ten  and  twenty-nine  years.  The  disease  did  not  .seem 
to  be  imported,  since  cases  were  returned  before  any  ships  arrived 
from  infected  countries,  although  after  the  importation  of  cases  it 
assumed  a  more  severe  form.  The  June  epidemic  seemed  to  confer 
a  certain  degree  of  immunity  during  the  second  outbreak  of  the 
disease  in  October. 

Erlendsson  reports  that  the  influenza  when  it  appeared  in  Iceland 
in  November,  1918,  corresponded  in  character  with  that  in  other 
portions  of  the  world.  Macklin  gives  an  interesting  description  of 
the  epidemic  as  it  occurred  in  Lapland.  The  onset  in  that  territory 
was  probably  in  November.  He  found  that  many  individuals  re- 
covered in  two  or  three  days  and  were  about  their  work  again  feeling 
perfectly  well.  If,  however,  they  contracted  pneumonia,  about  fifty 
per  cent.  died. 

"The  Laplanders  had  a  very  thorough  if  unsympathetic  way  of 
deahng  with  their  cases.  The  settlements  were  composed  of  wooden 
huts,  small  but  generally  well  made  and  warm.  A  common  type 
consisted  of  but  one  room,  used  by  the  family  for  all  purposes.  Better 
class  Laps  had  better  huts,  with  two  or  three  rooms.  In  each  settle- 
ment one  of  the  single-room  huts  had  been  set  apart,  and  into  this 
each  case  of  sickness  as  it  arose  was  unceremoniously  pushed;  and 
none  were  permitted  to  return  to  their  own  huts  until  completely 
recovered.  Whilst  there  they  received  practically  no  attention,  and 
no  healthy  person  ever  entered  to  attend  to  their  wants.  Occasion- 
ally a  bowl  of  water  or  reindeer  milk  was  hastily  passed  in  at  the  door, 
or  a  huge  chunk  of  reindeer  meat  thrown  in,  uncooked  and  uncarved. 

"We  visited  every  settlement  within  our  reach  and  entered  these 
huts.  The  stench  on  opening  the  door  met  one  like  a  poison  blast 
and  the  rooms  were  nearly  always  ill  lighted  and  dark.  The  patients 
lay  littered  about  the  floor  in  a  crowded  mass,  fully  dressed  in  clothes 


80  INFLUENZA 

and  boots  (most  of  them  had  no  socks),  and  with  no  other  cover  but 
an  occasional  greasy  rug.  Although  the  outside  air  was  cold  and  the 
ground  snow-covered,  the  temperature  inside,  maintained  by  the 
combined  mass  of  bodies,  was  generally  sufficiently  high.  The  patients 
in  these  huts  included  both  sexes  and  all  ages;  some,  when  we  entered, 
sat  up  and  with  flushed  faces  and  dull,  uncomprehending  eyes  watched 
us  listlessly.  Others  lay  restlessly  twisting  about,  quite  incapable 
of  taking  any  interest  or  of  answering  any  questions." 

The  epidemic  struck  Alaska  in  October,  invading  first  the  towns  of 
the  sea  coast,  being  very  evidently  brought  thither  by  steamer. 
Travel  to  the  interior  was  stopped  and  so  the  latter  escaped,  to  a  great 
extent,  the  outbreak.  At  Kodiak  and  on  Cook  Inlet,  the  mortaUty 
was  extremely  high.  Whole  villages  of  esquimaux  lost  their  entire 
adult  population.  Many  infants  were  frozen  in  their  dead  mothers' 
arms. 

Influenza  in  China. — We  have  been  able  to  follow  the  pandemic 
quite  consecutively  as  it  has  spread  around  the  world,  from  a  first 
outbreak  in  the  United  States  in  March,  1918.  We  repeat  that  the 
disease  was  presumably  present  in  Europe  and  elsewhere  previous 
to  that  time,  as  it  was  in  America,  but  the  particular  virus  which 
ultimately  acquired  sufficient  virulence  to  produce  the  pandemic  may 
well  be  that  which  came  from  North  America.  Did  this  virus  arise 
from  an  endemic  focus  in  this  continent,  or  was  it  transported  to  us  at 
a  somewhat  earUer  date  from  Asia? 

McNalty  states  that  influenza  was  present  in  China  and  in  the 
Japanese  Navy  in  March  of  1918.  He  gives  no  reference.  Carnwath 
makes  the  same  statement  and  gives  as  reference  the  report  of  Kabe- 
shima  and  Lee.  The  author  has  not  been  able  to  obtain  this  report. 
The  Health  Officer  of  Shanghai  made  the  following  report  for  May, 
1918:  "Towards  the  end  of  the  month,  reports  were  received  of 
outbreaks  of  'fever'  which  rapidly  affected  a  large  proportion  of  the 
employees  of  various  ofl&ces,  shops,  pohce  stations,  etc.  As  a  result  of 
clinical  and  laboratory  observations  of  cases  admitted  to  the  Chinese 
Isolation  Hospital  the  disease  was  recognized  as  epidemic  influenza. 
The  same  disease  was  reported  to  have  appeared  in  Peking  before 
reaching  Shanghai,  but  subsequent  reports  showed  that  most  of  the 
river  ports  were  almost  simultaneously  infected;  that  is  to  say  the 
rate  of  spread  conformed  to  the  rate  of  conveyance  by  railways  and 
boats  of  infected  persons;" 

In  November  of  1918  an  editorial  note  in  the  China  Medical 
Journal  reads  as  follows : 


AN    EPIDEMIOLOGIC    STUDY  81 

"From  nearly  all  parts  of  China  reports  are  being  sent  to  the  news- 
papers of  the  occurrence  of  a  severe  epidemic  of  disease  which  seems 
to  manifest  itself  in  various  forms.  In  Wusueh,  where  the  disease  is 
called  'the  five  days'  plague'  the  symptoms  are  said  to  be  not  unlike 
those  of  cholera,  death  in  some  cases  ensuing  in  less  than  a  day.  In 
other  cases  it  is  complicated  by  severe  and  often  fatal  pneumonia. 
At  Anking  many  cases  have  all  the  symptoms  of  typhoid  fever,  but 
the  mortality  is  great  and  sudden.  In  one  house  four  people  died 
within  a  few  hours  of  each  other,  and  in  another  house  eight  persons 
out  of  eleven  died.  At  Wuhu  and  other  of  the  lower  Yangtze  ports 
it  is  said  to  resemble  dengue  fever  and  the  mortality  is  so  great  that 
undertakers  are  finding  it  difficult  to  meet  the  demand  for  coffins.  In 
Shansi,  where  the  victims  literally  number  thousands,  the  disease 
is  regarded  as  influenza.  In  Peking  fully  fifty  per  cent,  of  the  Chinese 
have  been  affected  and  the  mortality  has  been  heavy.  Accurate 
reports  from  medical  men  in  these  cities  would  be  very  instructive." 

The  author  has  the  following  personal  communication  from  Doctor 
Arthur  Stanley  of  the  Health  Department  of  the  Shanghai  oMunicipal 
Council.  "Influenza  fever  appeared  during  the  recent  epidemic  in 
Shanghai  towards  the  end  of  May  1918.  It  swept  over  the  whole 
country  like  a  tidal  wave.  You  may  take  it  that  it  spread  like  most 
rapid  extant  means  of  transit.  A  primary  source  of  origin  was  not 
made  known." 

It  is  to  be  hoped  that  more  definite  and  concurrent  information 
will  be  forthcoming  in  the  case  of  China.  A  thorough  search  of  the 
literature  as  reviewed  for  China  and  Japan  in  the  China  Medical 
Journal  reveals  no  description  of  the  disease  previous  to  April  or 
May  of  1918.  Nevertheless  we  must  assume  that,  until  contradictory 
reports  are  made,  the  disease  was  present  in  those  countries  in  ]\Iarch  as 
stated  by  Camwath. 

Autumn    Spread    in    the    United    States. 

By  the  first  of  July,  1918,  convalescent  cases  of  influenza  began 
to  appear  among  members  of  the  crews  of  transports  and  other  vessels 
arriving  in  Boston  from  European  ports.  The  number  of  such  cases 
on  each  ship  was  usually  not  more  than  four  or  five,  but  Woodward 
records  that  in  one  or  two  instances  between  twenty  and  twentj'-five 
individuals  were  sick  on  incoming  vessels.  None  of  these  were 
seriously  ill,  none  were  sent  to  the  hospital,  and  none  died.  The 
disease  in  this  class  of  persons  did  not  become  severe  until  late  August. 
Woodward  has  found  on  inquiry  among  practising  physicians  that 


82  INFLUENZA 

typical  cases  of  influenza  were  seen  with  notable  frequency  in  private 
practice  in  the  vicinity  of  Boston  during  the  month  of  August,  and 
that  they  had  developed  no  serious  complications,  the  only  after  effect 
being  the  marked  prostration. 

These  mild  preliminary  cases  failed  to  attract  attention;  first, 
because  of  their  relative  scarcity,  and  second  because  of  their  benign 
character.  Public  attention  was  first  directed  to  the  influenza  in 
Boston  by  the  apparently  sudden  appearance  during  the  week  ending 
August  28th  of  about  fifty  cases  at  the  Naval  Station  at  Common- 
wealth Pier.  Within  the  next  two  weeks  over  2,000  cases  had  occurred 
in  the  Naval  forces  of  the  First  Naval  District.  One  week  later  there 
was  a  similar  sudden  outbreak  in  the  Aviation  School  and  among  the 
Naval  Radio  men  at  the  Massachusetts  Institute  of  Technology.  The 
first  death  in  Boston  was  reported  on  September  8th. 

The  peak  of  daily  incidence  in  Boston  occurred  around  the  first  of 
October.  In  the  week  ending  October  5th  a  total  of  1,214  deaths  from 
influenza  and  pneumonia  was  reported,  while  by  the  thirds-week  of 
October  this  total  had  fallen  to  less  than  600,  and  for  the  week  ending 
November  9th  was  down  to  47.  Around  November  15th  the  number 
of  cases  rather  suddenly  increased  and  this  recurrent  wave  lasted  for 
about  ten  days.  By  the  25th  the  rate  was  back  to  what  it  had  been 
around  the  first  of  the  same  month.  On  or  about  December  1st  the 
incidence  again  rose  and  continued  increasing  daily,  to  reach  its  peak 
in  a  severe  recrudescence  around  December  31st. 

There  are  conflicting  reports  concerning  the  date  of  first  appearance 
of  the  epidemic  at  Camp  Devens,  Massachusetts.  Woodward  says 
that  a  sudden  and  very  significant  increase  was  reported  during  the 
third  week  in  August  in  the  number  of  cases  of  pneumonia  occurring 
in  the  army  cantonment  at  Camp  Devens,  seeming  to  justify  the 
statement  that  an  influenza  epidemic  may  have  started  among  the 
soldiers  there  even  before  it  appeared  in  the  naval  forces.  Soper,  on 
the  other  hand,  as  well  as  Howard  and  Love  in  their  official  report, 
place  the  date  of  the  first  case  at  Devens  as  September  7th.  Soper 
remarks:  "The  Devens  epidemic  is  supposed  to  have  commenced  on 
September  7,  1918,  in  D  Company,  42d  Infantry.  On  that  date  a  case 
of  supposed  meningitis  was  sent  to  the  hospital  from  this  company; 
on  the  following  day  twelve  cases  were  sent  for  observation.  These 
proved  to  be  influenza.  By  the  16th  thirty-seven  cases  had  gone  from 
the  same  company."  Howard  and  Love  state,  ''The  first  authentic 
cases  of  virulent  influenza  of  the  great  autumn  pandemic  among 
troops  in  the  United  States  appeared  on  September  7,  1918,  at  Camp 


AN    KPIDEMIOLOGIC    STUDY  83 

Devens,  Mass."  These  statements  by  Howard  and  Love  do  not 
eliminate  the  possibility  of  earlier  and  less  virulent  unrecognized 
eases.  Wooley,  who  was  camp  epidemiologist,  reports  that  influenza 
began  at  Camp  Devens  on  the  8th  of  September,  1918.  It  reached 
its  acme  on  the  16th,  17th  and  18th  of  the  month  and  then  rapidly 
declined,  almost  completely  vanishing  about  the  middle  of  November. 
He  makes  no  observation  as  to  whether  a  mild  form  of  the  disease 
was  or  was  not  present  in  the  camp  in  March  and  April  preceding. 

Influenza  entered  Massachusetts  at  Boston.  Reeks  reports  that 
it  entered  Connecticut  at  New  London,  the  cases  coming  primarily 
from  the  experimental  station  and  from  Fort  Trumbull,  where  vessels 
from  foreign  ports  had  discharged  patients.  He  believes  that  the 
disease  was  first  introduced  by  ships  arri\'ing  in  New  London  from 
abroad  and  by  men  from  the  Boston  Navy  Yard,  but  numerous  foci 
developed  in  a  short  period  of  time  in  various  parts  of  the  state. 
Many  of  these  had  appeared  by  the  middle  of  September,  and  the 
source,  according  to  Winslow  and  Rogers,  was  traced  to  military 
establishments,  chiefly  Camp  Devens.  In  Wallingford,  Willimantic, 
Hartland,  Rockville  and  Danbury,  all  of  which  towns  were  attacked 
early  in  the  epidemic,  investigation  showed  that  the  disease  developed 
in  each  case  two  or  three  days  after  visits  of  soldiers  from  Camp 
Devens.  In  Connecticut  the  epidemic  spread,  beginning  at  New 
London,  chiefly  from  east  to  west,  reaching  its  peak  in  the  Eastern 
section  around  October  4th,  in  the  central  section  October  loth,  and 
in  the  Western  part  of  the  state  around  October  24th.  Towns  which 
had  been  infected  early  by  visitors  from  miUtary  estabhshments 
reached  the  climax  sooner  than  other  towns  nearby.  In  spreading 
from  New  London  north  and  west  the  large  cities  of  Connecticut  were 
successively  invaded,  New  Haven  and  Hartford  reaching  their  crest 
about  ten  days  later  than  New  London,  while  Fairfield  County  did  not 
reach  its  acme  until  later  than  New  Haven. 

In  the  cities  along  the  New  England  coast  we  see  then  that  the  dis- 
ease reached  epidemic  proportions  early  in  September.  By  September 
21st  it  had  become  epidemic  in  a  wide  area  along  the  Atlantic  coast 
extending  from  the  Southern  part  of  Maine  to  Virginia,  as  well  as  in  a 
number  of  localities  scattered  over  the  entire  country.  By  September 
28th,  areas  adjacent  to  the  centers  in  which  the  epidemic  had  already 
appeared  were  affected,  suggesting  radial  movement  from  these 
centers.  By  that  time  the  greater  part  of  the  New  England  States, 
the  North  Atlantic  and  Central  States,  and  some  of  the  Gulf  and 
Pacific  Coast  States  had  become  involved.  By  October  5th  the 
pandemic  had  apparently  reached  all  parts  of  the  country  with  the 


84  INFLUENZA 

exception  of  the  more  isolated  rural  districts  and  some  areas  in  the 
Central  States  and  Mountain  States.  Within  an  additional  ten  days 
even  these  areas,  with  the  exception  of  the  very  remote  rural  districts, 
had  been  reached  by  the  epidemic.  Within  four  weeks  the  disease 
had  become  distributed  to  all  sections  of  the  country,  and  within  six 
weeks  from  its  first  epidemic  prevalence  in  Boston  practically  the 
entire  country  had  been  invaded. 

Sydenstricker  in  a  preliminary  report  remarks  on  the  fact  that  the 
disease  reached  an  epidemic  stage  in  a  number  of  locaHties  in  the 
central,  northern,  southern  and  western  sections  at  about  the  same 
time  as  it  did  in  the  area  along  the  northeastern  coast.  "The  possi- 
bihty  is  suggested,  therefore,  that  sources  of  infection  existed  in  at 
least  some  of  the  larger  population  centers,  well  distributed  through 
the  country,  some  time  before  the  disease  appeared  as  a  nation-wide 
epidemic.  The  apparent  radial  spread  of  the  epidemic  from  certain 
centers  would  seem  to  strengthen  this  hypothesis.  It  may  also  be 
noted  that  there  is  evidence,  the  collection  of  which  has  not  yet  been 
completed,  pointing  to  the  existence  of  cases  of  the  disease  in  various 
centers,  probably  widely  distributed,  weeks  before  they  were  definitely 
recognized  as  influenza.  The  possibility  that  these  foci  themselves 
had  a  common  focus  is  by  no  means  excluded,  of  course,  but  there  is  as 
yet  no  conclusive  evidence  that  would  warrant  the  statement  that  the 
starting  point  of  the  epidemic  was  Boston  or  any  specific  locality." 

Dublin,  from  a  study  of  the  statistics  of  the  Metropolitan  Life 
Insurance  Company,  finds  that  the  virulence  of  the  infiuenza,  as 
indicated  by  the  mortality  rate,  was  greatest  along  the  Atlantic  Coast 
and  became  progressively  less  as  it  progressed  westward.  There  was 
one  exception.  The  mortality  was  high  in  San  Francisco,  higher  than 
in  other  western  communities.  Dublin  beheves  that  quite  possibly 
there  was  a  double  infection  in  San  Francisco  in  the  fall  of  1918,  one 
coming  from  the  East  and  of  small  caliber,  while  the  other  came  either 
by-way  of  the  Panama  Canal  or  perhaps  from  Asia.  The  evidence  in 
favor  of  two  ways  is  that  Dublin  finds  that  the  peak  of  incidence  in 
San  Francisco  and  in  some  other  places  on  the  Pacific  Coast  occurred 
sometime  in  advance  of  the  siniilar  peak  at  points  inland  from  the 
coast.  This  is  not  brought  out  in  Pearl's  chart,  and  the  latter  finds 
when  considering  the  peak  of  deaths  that  the  peak  for  San  Francisco 
was  late.  The  peak  in  that  city,  in  Oakland,  California,  and  in  Los 
Angeles,  was  reached  on  the  week  ending  November  2d.  Few  cities 
had  as  late  death  peaks.  Cleveland  and  Pittsburgh  reached  their 
peak  in  the  same  week,  St.  Paul,  Minnesota  in  the  week  ending 
November  16th,  and  St.  Louis,  Milwaukee  and  Grand  Rapids  not  until 


AN    EPIDEMIOLOGIC    STIDV  »5 

the  week  ending  December  14th.  In  the  case  of  Alilwaukee  and  St. 
Louis  these  were  the  high  peak  dates  but  they  were  second  peaks. 
In  the  former  the  first  peak  occurred  October  26th  and  in  the  latter 
November  2d.  In  Grand  Rapids  the  increase  in  mortaHty  was  clear- 
cut  by  the  middle  of  October,  although  the  peak  was  not  reached  until 
the  week  ending  December  14th.  These  statistics  would  indicate 
that  San  Francisco  was  attacked,  as  evidenced  by  increase  in  death 
reports,  relatively  late,  and  at  about  the  time  that  would  be  necessary 
for  the  disease  to  be  carried  across  the  continent. 

In  an  article  by  Ely,  Lloyd,  Hitchcock  and  Nickson  it  is  said  that 
influenza  first  appeared  in  the  Puget  Sound  Navy  Yard,  near  Seattle, 
on  September  17,  1918,  and  that  it  was  introduced  by  a  draft  of  987 
sailors  received  from  Philadelphia,  a  number  of  whom  arrived  ill,  or 
came  down  within  a  few  hours  after  reaching  their  destination.  As  a 
result,  Seattle  and  the  State  of  Washington  were  infected  somewhat 
ahead  of  the  other  West  Coast  States.  According  to  the  record, 
influenza  did  not  assume  epidemic  proportions  in  the  State  of  Oregon 
for  nearly  a  month  after  this  Navy  Yard  epidemic. 

With  army  camps  and  cantonments  situated  in  nearly  every  section 
of  the  country  it  is  difficult  to  follow  the  general  direction  of  spread 
from  camp  to  camp.  During  the  period  of  the  epidemic,  troop  move- 
ments were  in  general  from  West  to  East  toward  points  of  embarkation 
rather  than  in  the  reverse  direction.  This  was  in  the  opposite  direction 
to  that  taken  by  the  pandemic.  Away  from  the  coast  there  were, 
however,  many  movements  of  troops  from  camp  to  camp,  in  the  redis- 
tribution of  forces.  That  these  troop  movements  were  not  discon- 
tinued during  the  epidemic  is  indicated  by  the  report  of  Howard  and 
Love:  "The  virulent  type  of  influenza  had  spread  rapidly  from  camp 
to  camp,  from  the  Atlantic  seaboard  to  the  South  and  West,  due  to  the 
continual  interchange  of  personnel  from  infected  to  non-infected  camps. 
Such  movements  of  troops  at  this  time  were  recognized  as  dangerous 
and  inadvisable,  and  prompt  recommendations  were  made  by  the 
Medical  Department  that  such  movements  be  discontinued  or  greatb^ 
restricted,  if  compatible  with  military  interests,  which,  of  course, 
were  at  the  time  paramount.  The  War  Department  was  unable  to 
approve  any  marked  restriction  of  movement  of  men  from  camp  to 
camp  at  this  time.  One  result  of  the  free  inter-communication  of 
military  personnel  was  that  practically  all  military  stations  in  the 
United  States  were  in  the  throes  of  the  epidemic  at  the  same  time." 

In  addition  to  this  means  of  inter-communication  we  had  the  possi- 
bility of  spread  to  the  various  camps  by  the  ordinary  course  of  civilian 
and  commercial  travel  as  in  spread  to  different  communities,  and  also 


86 


INFLUENZA 


the  possibility  of  importing  large  amounts  of  virus  at  one  time  on  the 
incoming  trains  with  new  draft  troops. 

Soper  gives  the  following  order  for  camps  attacked : 


Order. 

Camp. 

Location. 

Date. 

1 

Devens 

Massachusetts 

Sept.  12 

2 

Upton 

New  York 

Sept.  13 

3 

Lee 

Virginia 

Sept.  17 

4 

Dix 

New  Jersey 

Sept.  18 

4 

Jackson 

South  Carolina 

Sept.  18 

5 

Hoboken 

New  Jersey 

Sept.  19 

5 

Syracuse 

New  York 

Sept.  19 

5 

Gordon 

Georgia 

Sept.  19 

5 

Humphreys 

Virginia 

Sept.  19 

6 

Logan 

Texas 

Sept.  20 

6      . 

Funston 

Kansas 

Sept.  20 

6 

Meade 

Maryland 

Sept.  20 

7 

Grant 

Illinois 

Sept.  22 

7 

Taylor 

Kentucky 

Sept.  22 

.  8 

Sevier 

South  Carolina 

Sept.  23 

8 

Lewis 

Washington 

Sept.  23 

8 

Newport  News 

Virginia 

Sept.  23 

9 

Pike 

Arkansas 

Sept.  24 

10 

Beauregard 

Louisiana 

Sept.  25 

10 

Eustis 

Virginia 

Sept.  25 

11 

Greene 

North  Carolina 

Sept.  26 

11 

McClellan 

Alabama 

Sept.  26 

12 

Kearney 

California 

Sept.  27 

12 

Bowie 

Texas 

Sept.  27 

13 

Johnston 

Florida 

Sept.  28 

13 

Sheridan 

Alabama 

Sept.  28 

.     14 

Sherman 

Ohio 

Sept.  29 

14 

Dodge 

Iowa 

Sept.  29 

14 

Shelby 

Mississippi 

Sept.  29 

15 

Custer 

Michigan 

Sept.  30 

16 

Travis 

Texas 

Oct.      1 

•  17 

Cody 

New  Mexico 

Oct.      3 

18 

Forrest 

Georgia 

Oct.      6 

19 

Mac  Arthur 

Texas 

Oct.      7 

20 

Wadsworth 

South  Carolina 

Oct.    11 

20 

Wheeler 

Georgia 

Oct.    11 

20 

Greenleaf 

Georgia 

Oct.    11 

AX    EPIDEMIOLOGIC    STUDY  87 

Howard  and  Love  have  established  definitely  that  the  extension  of 
the  virulent  influenza  from  Camp  Devens  to  other  camps  south  and 
west  in  September,  1918,  can  be  traced  in  many  instances  directly 
to  the  interchange  of  military  personnel  from  infected  to  non-infected 
camps.  The  height  of  the  September  outbreak  in  the  United  States 
Army  extended  over  a  period  of  about  nine  weeks,  from  Sept.  13th  to 
November  15th,  and  during  this  period  over  20,000  deaths  occurred 
among  troops  in  the  United  States  alone  in  excess  of  the  number  that 
would  have  occurred,  if  the  disease  death  rate  for  the  corresponding 
period  of  the  preceding  year  had  prevailed. 

It  is  interesting  to  note  with  respect  to  Camp  Humphreys,  Virginia, 
that  there  were  possibly  some  sporadic  cases  previous  to  the  autumn 
outbreak.  Brewer  in  reporting  on  the  epidemic  in  September  and 
October  records  the  first  case  as  having  occurred  shortly  after  July 
1st.  He  makes  no  mention  of  there  having  been  any  outbreak  what- 
ever prior  to  that  date.  Between  July  1st  and  September  12th  there 
were  only  sporadic  cases  diagnosed  as  influenza.  The  autumn  out- 
break began  at  Camp  Humphreys  September  13th  and  ended  October 
18th. 

Recrudescences. 

"We  have  already  seen  from  the  work  of  Pearl  that  recrudescences 
following  the  original  spread  in  any  one  locality  were  the  rule  rather 
than  the  exception  in  this  country.  He  found  that  in  sixty-five  per 
cent,  of  the  forty  cities  studied  there  were  two  distinct  peaks  in  the 
mortality  curve  and  in  twenty  per  cent,  there  were  three,  while  only 
fifteen  per  cent,  had  but  one  peak.  The  first  peak  was  as  a  rule  the 
highest.  Although  there  was  no  absolute  regularity  in  the  time  of 
occurrence  of  the  recrudescences.  Pearl  estabhshed  that  the  high-peak 
cities  had  the  second  peaks  on  an  average  7.1  weeks  after  the  first,  and 
the  third  peak  on  an  average  13.1  weeks  after  the  second.  The  two- 
peak  cities  are  divided  into  two  classes,  the  first  comprising  about  a 
third  of  the  total  number,  had  the  second  mortality  peak  around  eight 
weeks  after  the  first,  while  the  remaining  two-thirds  had  the  second 
peak  about  thirteen  weeks  after  the  first.  The  cycle  in  the  epidemic 
wave  appears  to  be  nearly  a  multiple  of  seven  weeks.  He  suggests 
that  the  smaller  group  of  two  peak  cities  with  early  second  peak  may 
have  been  cities  which  at  the  time  were  presumably  destined  to  show  a 
third  distinct  wave  and  peak  of  mortality,  but  in  which  for  some  reason 
not  now  apparent  the  third  wave  did  not  eventuate.  In  contradis- 
tinction the  larger  group  of  two-peak  cities  with  the  second  peak 


88  INFLUENZA 

occurring  around  thirteen  weeks  after  the  first  are  presumably  cities 
in  which  the  complex  of  factors  determining  the  form  of  the  mortality 
curve  was  such  as  to  lead  definitely  to  a  two  and  only  two-peak  curve. 
In  three-peak  cities  the  first  interval  was  around  seven  weeks,  the 
second  around  thirteen  weeks.  The  two-peak  cities  with  an  interval 
around  thirteen  were  probably  not  destined,  according  to  Pearl,  to 
have  another  repetition,  but  those  with  an  interval  of  seven  were 
presumably  destined  to  have  a  second  interval,  the  thirteen-week 
interval,  which  for  some  reason  did  not  occur. 

This  raises  the  question  of  periodicity,  a  subject  which  we  will 
discuss  at  a  more  appropriate  place. 

This  experience  of  recrudescences  was  similar  in  the  American 
Expeditionary  Forces.  The  first  outbreak  lasted  through  April  and 
May  and  into  June.  The  second  came  in  September  and  October. 
The  spring  epidemic  had  been  characterized  by  mildness  and  was 
known  as  three-day  fever,  but  in  the  autumn,  complications  of  the 
respiratory  tract  predominated  in  the  symptom  complex.  By  August 
18th  a  severe  epidemic  had  occurred  in  an  artillery  camp  at  La  Valda- 
hon  in  the  Jura  Mountains,  near  Bezangon.  Early  in  September  a 
larger  epidemic  occurred  in  an  artillery  camp  near  Bordeaux.  The 
epidemic  in  our  troops  in  France,  as  well  as  in  the  French  civil  and 
mihtary  population,  reached  its  height  during  October.  The  Service 
of  Supply  was  more  heavily  affected  than  were  the  troops  situated  on 
the  battle  front.  The  morbidity  rate  appeared  to  have  been  almost 
the  same  as  that  in  the  United  States.  That  it  was  not  quite  as  high 
has  been  shown  by  Howard  and  Love.  Longcope  states  that  it  pre- 
vailed particularly  among  the  troops  at  the  base  ports  where  during  a 
part  of  the  epidemic  transports  laden  with  infected  troops  were  being 
landed;  in  those  organizations  which  contained  the  largest  number  of 
replacement  troops;  and  in  organizations  being  moved  on  troop  trains, 
where  the  men  were  necessarily  closely  crowded. 

The  second  outbreak  subsided  during  the  early  part  of  November. 
A  third  occurred  in  January  and  February,  very  much  as  it  had  done  in 
the  United  States.  In  the  interval  between  the  second  and  third 
recurrences  there  was  no  time  at  which  the  entire  Expeditionary  Forces 
were  free  from  the  disease.  The  author  had  occasion  to  study  an 
outbreak  occurring  early  in  December  in  the  26th  Division  stationed 
in  rest  area  at  Montigny-le-Roi.  In  this  outbreak  the  respiratory 
comphcations  predominated,  as  in  October,  and  the  mortahty  was 
comparatively  high.  We  had  had  occasion  to  study  the  same  disease 
at  Camp  Sevier,  South  CaroHna  in  September  and  early  October,  1918, 


AX    EPIDEMlOLOtac    STLDY  89 

and  in  two  diffcront  localities  in  France  in  Docenii)er,  1918,  and  Feb- 
ruary, 1910,  and  found  that  the  clinical  characteristics  wen;  identical 
on  both  continents. 

The  more  severe  recurrence  in  England,  in  October,  has  been  care- 
fully studied.  In  fact  this  recurrence  was  almost  universal  in  all 
countries.  The  autumn  epidemic  has  been  reported  as  being  at  its 
height  in  October,  1918,  in  such  widely  separated  localities  as  the 
United  States,  England,  France,  Greece,  Brazil,  India,  Japan  and 
Korea. 

In  Europe  at  any  rate  the  third  wave  occurring  in  the  winter  of 
1919  was  quite  generally  distributed.  At  about  the  same  time  the 
disease  broke  out  in  England,  making  a  third  wave  in  less  than  a  year. 
Once  again  the  third  attack  began  less  suddenly  and  less  violently  and 
resulted  in  a  lower  number  of  fatalities.  During  February  there  was 
reported  to  have  been  a  great  increase  in  the  number  of  cases  in  Paris. 
It  had  terminated  by  March  27,  1919.  In  March  the  disease  broke 
out  anew,  this  time  assuming  grave  proportions,  not  only  in  that  city 
but  in  several  of  the  Departments. 

The  second  recrudescence  has  also  been  reported  as  being  present 
in  Spain. 

On  May  5,  1919,  report  was  received  from  Buenos  Ayres  that  in 
one  of  the  concentration  zones  for  naval  troops  located  in  the  harbor 
there  had  been  an  epidemic  of  short  duration,  but  with  high  morbidity, 
with  two  hundred  cases  being  frequently  reported  each  day. 

Just  as  Pearl  has  observed  a  certain  periodic  recrudescence  in  the 
United  States,  there  has  been  described  a  similar  periodicity  in  England. 
The  interval,  however,  is  described  as  twelve  weeks.  The  first  wave 
began  in  July  and  died  down  about  the  end  of  August,  running  a  two 
months  course.  Twelve  weeks  after  the  commencement  of  the  first 
wave,  at  the  beginning  of  October,  the  second  appeared.  It  had  disap- 
peared around  the  middle  of  December.  Again,  twelve  weeks  from 
the  beginning  of  the  second  wave,  that  is,  in  January,  the  third 
appeared. 

Recurrences  in  Winter  of  1919-1920. 

We  distinguish  between  the  flareups  following  the  autumn  spread 
of  1918,  and  which  lasted  until  the  spring  of  1919,  and  j'et  another 
widely  distributed  recurrence  in  the  winter  of  1920.  We  have  called 
the  former  recrudescences  to  distinguish  them  in  point  of  time  from  the 
latter,  but  do  not  imply  thereby  any  difference  in  the  character  or 
origin  of  the  secondary  waves.     Between  them  all  there  occurred 


90  INFLUENZA 

almost  continuously  isolated  or  solitary  cases  of  influenza  which 
served  to  keep  the  fires  smouldering.  In  our  own  work  in  the  city 
of  Boston  we  found  record  of  scattered  infrequent  cases  of  clinical 
influenza  of  apparently  low  infectivity  in  every  month  from  March, 
1919,  until  the  recurrence  in  January,  1920. 

Moreover,  in  some  localities  there  were  during  this  interval  small 
epidemic  outbreaks.  Thus  a  report  from  Lisbon,  Portugal,  on  June 
1,  1919,  states  that  the  deaths  from  influenza  in  that  city  during  the 
preceding  two  weeks  had  been  more  than  the  total  deaths  from  all 
causes  during  the  preceding  four  months.  A  report  from  London, 
October  30,  1919,  states  that  during  the  preceding  few  weeks  there 
had  been  in  the  ninety-six  great  towns  of  England  and  Wales  a  slight 
but  gradual  increase  in  the  number  of  deaths  attributed  to  the  disease, 
and  a  coincident  rise  in  the  number  of  notifications  of  acute  primary 
and  acute  influenzal  pneumonia.  The  feeling  at  that  time  was  that 
the  increase  was  associated  with  prevailing  meteorological  conditions, 
and  did  not  apparently  signify  more  than  the  usual  variation  in  respira- 
tory diseases  which  was  to  be  expected  at  that  season  of  the  year. 
On  November  3,  1919,  the  disease  was  reported  prevailing  at  Chile 
and  it  was  spreading  throughout  Boliva.  At  the  same  time  influenza 
had  spread  over  the  entire  country  surrounding  Buenos  Aires  and  had 
even  reached  the  neighboring  city  of  Montevideo.  In  the  latter  part 
of  November  more  than  2,000  cases  had  been  reported  at  Lemaies, 
about  fifteen  miles  northeast  of  Granada,  Spain. 

The  winter  of  1920. — In  the  United  States  the  death  rates  from 
influenza  and  pneumonia  in  the  large  cities  over  the  entire  country  were 
below  the  usual  average  from  May,  1919,  until  January  1,  1920.  In 
the  week  ending  January  17th  there  was  a  sharp  increase  in  the  influ- 
enza-pneumonia rate,  which  occurred  simultaneously  in  Kansas  City 
and  Chicago.  In  the  latter  city  an  excess  over  the  average  was  not 
reached  until  some  days  later,  but  the  maximum  mortality  occurred 
in  the  week  ending  January  31st,  while  in  Kansas  City  the  mortality 
did  not  reach  its  height  until  one  week  later.  New  York,  Washington, 
San  Francisco,  Milwaukee  and  St.  Paul  soon  followed  with  an  increase 
in  the  week  ending  January  24th,  and  in  the  subsequent  two  weeks 
many  other  cities  were  added  to  the  list.  By  February  14th  thirty- 
two  out  of  the  thirty-six  large  cities  reporting  had  an  increase  in  the 
death  rate  from  influenza  and  pneumonia  as  compared  with  the  same 
period  in  1917.  The  maximum  was  reached  at  this  time,  and  accord- 
ing to  the  Bureau  of  the  Census  reports  there  were  7,059  deaths  from 
influenza  and  pneumonia  during  the  week  ending  February  14th.     In 


AN    EPIDEMIOLOGIC    STUDY  91 

the  next  week  the  number  of  deiiths  from  these  causes  in  the  cities 
reporting  had  dropped  to  5,088.  The  February  weekly  average  for 
1917  was  1,489.  In  the  week  ending  February  14th,  267,643  cases 
of  influenza  were  reported  from  forty-one  states;  the  excess  annual 
death  rate  as  compared  with  the  average  for  the  period  from  1910 
to  1916  was  1,319. 

In  general  the  1920  recurrence  was  decidedly  milder  than  the 
autumn  outbreak  of  1918.  Certain  cities,  however,  suffered  severely, 
particularly  Detroit,  Milwaukee,  Kansas  City,  Minneapolis  and  St. 
Louis.  In  these  the  death  rate,  while  the  epidemic  lasted,  was  higher 
than  that  of  1918.  The  duration  of  the  epidemic  was  generally, 
however,  shorter  in  these  cities.  Columbus,  Ohio,  and  Indianapolis 
sufifered  severely,  but  to  a  less  extent  than  the  cities  just  mentioned. 
In  Chicago  the  death  rate  was  not  as  high  as  in  the  fall  of  1918,  but 
it  did  rise  far  above  the  point  reached  during  the  1889-90  outbreak, 
and  the  influenza  in  the  last  two  weeks  of  January  brought  the  total 
mortality  for  that  month  up  to  5,149,  the  highest  mortality  in  the 
history  of  the  city  with  the  exception  of  October,  1918. 

We  have  already  discussed  the  recurrent  epidemic  as  it  was  studied 
in  Detroit.  The  salient  characteristics  were  a  rapid  and  fairly  sym- 
metrical evolution,  a  shorter  duration  than  in  1918,  a  lower  morbidity 
with  a  higher  mortality  rate,  and  finally,  a  smaller  total  number  of 
deaths  than  in  1918. 

The  1920  recurrence  was  widespread.  It  was  not  confined 
entirelj^  to  the  large  cities.  Semi-official  reports  from  small  towns  and 
villages  show  very  much  the  same  conditions  as  were  observed  in  the 
larger  cities.  On  the  whole,  however,  most  communities,  both  large 
and  small,  suffered  less  severely  than  in  the  first  spread.  The  few 
exceptions  to  this  were  distributed  over  the  continent  without 
uniformity. 

The  first  among  the  large  cities  to  show  an  increase  in  death  rate 
from  the  epidemic  was  Kansas  City,  in  which  the  mortality  first 
climbed  in  the  week  ending  January  17th.  The  following  week  there 
was  an  increased  rate  in  Chicago,  New  York  and  Milwaukee,  and  one 
week  later,  Boston,  Detroit,  San  Francisco  and  Philadelphia  were 
affected.  New  Orleans  was  one  of  the  last  large  cities  affected,  not 
showing  a  definite  increase  until  the  week  ending  February  14th.  In 
contrast  to  the  1918  pandemic,  the  influenza  of  1920  showed  no  clear- 
cut  direction  of  spread,  and  was  as  in  the  years  following  1889  due, 
without  doubt,  to  firing  up  of  the  pandemic  virus  as  it  had  been  left 
scattered  in  many  endemic  foci  throughout  the  earth.     There  probably 

8 


92 


INFLUENZA 


were  instances  of  spread  from  the  larger  centers  to  outlying  districts, 
but  there  was  no  continuous  spread  over  large  areas.  The  accompany- 
ing table  shows  clearly  that  the  disease  this  year  commenced  in  the 
center  of  the  continent,  a  fact  which  would  seem  to  disconnect  it  entirely 
from  the  late  epidemics  of  1919,  occurring  in  Europe: 

Annual  death  rates  from  all  causes  by  week  in  certain  large  cities  oj  the   United 
States  from  week  ending  January  3d  to  week  ending  February  21st. 


Week  Ending 

City. 

January. 

February. 

3 

10 

17 

24 

31 

7 

14 

21 

Kansas  City 

Chicago 

16.3 

14.4 
14.0 
11.6 
13.7 
16.8 
16.5 
15.6 
18.8 

15.8 
13.8 
15.3 
12.5 
13.0 
16.9 
15.4 
16.7 
19.6 

19.3 
15.1 
14.6 
9.0 
14.2 
14.1 
19.6 
16.2 
22.6 

32.7 
23.5 
19.5 
15.6 
15.5 
16.8 
19.2 
16.8 
18.8 

39.5 

41.3 
28.0 
29.4 
33.9 
20.3 
22.9 
18.3 
20.9 

61.5 
39.1 
35.0 
34.5 
60.9 
27.1 
25.2 
22.1 
20.1 

44.0 
24.6 
35.1 
27.1 
42.9 
33.7 
31.8 
34.3 
25.0 

29.1 

17.7 

New  York 

Milwaiikee 

24.8 
16.9 

Detroit 

21.6 

Boston 

32.1 

San  Francisco 

Philadelphia 

28.8 
37.2 

New  Orleans 

32.3 

The  relative  severity  of  the  two  epidemics  in  certain  of  the  large 
cities  has  been  compared  by  H.  F.  Vaughan,  and  he  has  found  as  is  seen 
by  the  table  that  Kansas  City  and  Detroit,  two  of  the  early  cities 
affected,  had  the  highest  mortality  in  1920.  Philadelphia  in  1918  lost 
nearly  three  times  as  many  people  as  Detroit  did  in  1920.  Detroit 
was  higher  than  Chicago  in  1920,  but  lower  in  1918. 

Per  cent,  of  population  killed  by  influenza.    . 


1920. 

1918-1919. 

First  seven  weeks. 

First  seven  weeks. 

Twenty-one  weeks. 

Detroit 

0.20 
0.12 
0.24 
0  10 

0.17 
0.34 
0.30 
0  76 

0.28 

Chicago . .  . 

0.41 

Kansas  City 

0.63 

Philadelphia 

0.82 

New  Orleans 

0.05            1            0.55 

0.77 

The  following  table  taken  from  the  'Tinal  InJBuenza  Bulletin,"  by 
E.  R.  Kelley,  Commissioner  of  Health  in  Massachusetts,  shows  dis- 
tinctly the  difference  that  must  be  always  borne  in  mind  between 
curves  of  influenza  incidence  and  death  curves.  In  his  table  the 
mortality  climbed  first  on  the  week  ending  January  13th,  as  in  the  table 


AN    EPIDEMIOLOGIC    STUDY 


93 


above,  but  the  incroaso  in  influonza  cases  began  at  least  one  week 
earlier.  It  is  characteristic  of  influenza  epidemics  that  the  rise  of 
mortality  curves  follows  that  of  morbidity  by  about  a  week: 


Influenza  and  -pneumonia  cases  in  Massachusetts  in  / 

he  first  three  months  of  1920. 

Influenza. 

Lobar  pneumonia. 

Cases. 

Deaths. 

Cases.         Deaths. 

Week  ending  January  3d 

Week  ending  January  10th 

41 

46 

58 

489 

4,495 

9,627 

10,747 

5,601 

2,375 

1,144 

490 

254 

147 

218 

0 
2 

0 

4 

48 

272 

133 

181 

147 

54 

31 

20 

14 

6 

109 
142 
145 
201 
313 
382 
583 
510 
313 
206 
130 
105 
102 
97 

9 
50 

Week  ending  January  17  th 

Week  ending  January  24th 

52 
56 

Week  ending  January  31st 

96 

Week  ending  February  7th 

Week  ending  February  14th 

Week  ending  February  21st 

Week  ending  February  28th 

Week  ending  March    6th 

Week  ending  March  13th 

212 
140 
147 
114 
34 
54 

Week  ending  March  20th 

44 

Week  ending  March  27th 

94 

Week  ending  April  3d 

12 

In  Massachusetts  in  the  first  three  months  of  1920  there  were 
reported  35,633  cases  of  influenza  and  3,158  of  lobar  pneumonia,  with 
906  deaths  from  the  former  disease  and  1102  from  the  latter.  The 
case  rate  per  100,000  from  influenza  was  883.4;  from  lobar  pneumonia, 
78.3;  the  death  rate  from  influenza,  22.4;  from  lobar  pneumonia,  27  .4; 
and  the  fatahty  per  cent,  from  the  former  disease  was  2.5,  and  from 
the  latter,  34.9. 

The  epidemics  in  Detroit  and  Boston  both  showed  a  symmetrical 
evolution  and  a  single  wave.  This  appears  to  have  been  the  more 
frequent  type  of  recurrence  in  this  country.  There  are  examples  of 
the  secondary  curve.  At  the  Great  Lakes  Naval  Training  Station 
the  epidemic  began  during  the  week  ending  January  17th.  On 
January  12th  there  were  fifty-one  cases.  The  peak  was  reached  on  the 
third  day  with  the  admission  of  182  new  cases  during  twenty-four 
hours.  Although  the  peak  came  early  the  decline  was  less  rapid  and 
there  were  four  secondary  peaks,  but  the  outbreak  terminated  on  the 
twentj^-fourth  day.  On  the  whole  the  epidemic  was  less  severe  than 
in  1918.  Pneumonia  was  a  complication  in  about  ten  per  cent,  of  the 
reported  cases  of  influenza  at  the  training  station. 

On  the  European  continent  there  were  similar  recurrences  in  the 
first  three  months  of  1920.     In  the  large  towns  of  England  the  recorded 


94  INFLUENZA 

deaths  from  influenza  made  an  increase  in  a  steady  curve  from  sixty- 
six  in  the  last  week  of  January  until  the  week  ending  March  27th. 
After  that  date  there  was  a  gradual  falling  off.  That  the  situation 
was  in  no  way  as  serious  as  it  was  at  the  same  time  in  the  American 
cities  and  in  certain  other  parts  of  Europe  is  indicated  by  an  annota- 
tion in  the  Lancet  of  March  6th.  According  to  this  annotation,  the 
weekly  totals  of  deaths  attributed  to  influenza  in  London  and  the  96 
great  towns  had  on  the  whole  tended  to  increase  in  the  early  part  of 
1920,  but  the  absolute  increment  was  so  small  and  the  necessary 
uncertainty  of  classification  so  great  that  no  unfavorable  inferences 
could  be  drawn  from  these  fluctuations  alone.  On  the  other  hand,  the 
notifications  of  cases  of  pneumonia  increased  appreciably,  too  much  to 
be  set  down  as  a  mere  chance  fluctuation.  But  notification  for  this 
disease  had  not  been  in  force  long  enough  to  enable  accurate  compari- 
son. There  were  no  indications  of  epidemic  influenza  in  any  of  the 
large  factories  situated  throughout  the  country.  But  on  the  other 
hand  there  was  proof  of  the  existence  of  epidemic  influenza  of  an 
infectious,  but  relatively  non-fatal  type  in  certain  large  schools  situated 
in  the  South  and  Southwest  of  England. 

The  annotation  concludes  that  influenza  was  epidemic  in  a  few 
localized  English  and  Welsh  communities,  and  that  the  type  was 
similar  to,  but  less  severe  than  that  of  1918-19. 

In  the  city  of  Paris  between  the  11th  and  31st  of  January  there 
was  a  very  definite  increase  in  the  death  rate  from  inflammation  of  the 
respiratory  tract  above  the  average  for  other  years. 

Renon  and  Mignot  studied  141  cases  of  influenza  (71  men  and  70 
women)  during  January  and  February,  1920,  at  L'Hopital  Necker. 
Fifteen  of  the  141  died.  According  to  these  observers  the  grip  of 
1920  attacked  all  ages  in  contradistinction  to  the  1918  epidemic  which 
affected  especially  the  young  and  vigorous.  One-third  of  their  group 
were  over  forty  years  of  age,  while  some  were  seventy  and  eighty  years 
old.  In  spite  of  this  the  disease  remained  relatively  mild.  Sixty- 
four  were  cases  of  simple  grip.  Forty-three  had  associated  bronchitis 
and  pulmonary  congestion  and  edema.  Twenty-seven  had  pneu- 
monia. One  had  acute  pulmonary  edema.  There  were  cases  of 
influenza  in  tuberculosis  individuals.  One  developed  an  acute  sero- 
fibrinous pleurisy.     One  had  purulent  pleurisy,  and  one  meningitis. 

In  Copenhagen  there  occurred  between  the  18th  and  24th  of 
January,  1920,  1,204  cases  of  influenza  with  four  deaths;  in  the  follow- 
ing week,  from  the  25th  to  the  31st  of  January,  7,445  cases  with  forty- 
two  deaths;  from  the  1st  to  the  7th  of  February,  11,038  cases  with  207 


AN    EPIDEMIOLOGIC    STUDY  95 

deaths;  from  the  8th  to  the  14th  of  February,  8,308  cases  and  327 
deaths.  This  is  to  be  contrasted  with  the  month  of  December,  1919, 
in  which  there  were  1,845  cases  of  influenza  in  Denmark,  of  which  only 
272  were  at  Copenhagen.  In  Christiania,  Norway,  during  the  week 
of  January  25th  to  31st.  there  occurred  eleven  deaths  from  influenza, 
whereas  during  the  preceding  two  weeks  there  had  not  been  a  single 
death  from  this   disease. 

In  December,  1919,  there  were  reported  in  Switzerland  only  511 
cases  of  influenza.  During  the  month  of  January,  1920,  this  increased 
to  13,162,  and  in  February  to  83,008,  the  estimated  population  being 
4,000,000.  From  February  the  disease  decreased  in  prevalence.  In 
Zurich,  with  a  population  of  210,000,  the  epidemic  resulted  in  14,534 
cases.  The  first  increase  began  around  January  4th.  The  total 
number  of  cases  for  January  was  1,071.  In  February  the  records  of  the 
four  weeks  showed  2,721,  4,140,  3,341  and  1,899  cases,  respectively; 
in  March  the  decrease  was  rapid,  886,  442  and  45  cases  being  reported 
in  the  first  three  weeks.  The  total  number  of  deaths,  mostly  due  to 
pneumonia,  was  229,  a  mortality  of  1.5  per  cent. 

During  1920  epidemics  were  also  observed  in  Valencia,  Santander 
and  other  towns  in  Spain,  and  in  Mexico  City.  In  the  latter  city  the 
number  of  deaths  was  reported  as  1,649,  as  contrasted  with  3,000  in 
1918. 

iNCtHBATION    PERIOD. 

An  accurate  determination  of  the  period  of  incubation  in  influenza 
presents  great  difficulties.  The  large  number  of  cases  with  the  conse- 
quent multiple  opportunities  for  infection  in  the  case  of  every  indi- 
vidual add  to  the  difficulty.  Under  any  circumstances  the  period  is 
very  short.  Parkes,  many  years  before  the  1889  epidemic,  beheved 
that  an  incubative  period  sometimes  exists;  that  it  was  sometimes 
very  short  and  sometimes  of  many  days  duration. 

"In  the  Transactions  of  the  College  of  Physicians  it  is  stated  that 
in  the  epidemic  of  1782,  seventeen  persons  came  to  London  to  an 
hotel,  and  on  the  following  day  three  were  attacked  with  influenza. 
Haygarth  says  that  a  gentleman  came  to  Chester  from  London,  on 
the  24th  of  May,  1782,  ill  of  influenza;  a  lady,  into  whose  family  he 
came,  was  seized  on  the  26th,  and  was  the  first  case  in  the  town. 
Haygarth  states,  evidently  with  the  view  to  point  out  the  possibility 
of  a  direct  contagion,  that  the  gentleman  was  engaged  to  be,  and  was 
afterwards,  married  to  this  lady.  In  this  case  the  longest  possible 
incubative  period  was  two  days.     In  1782  a  family  landed  at  Harwich, 


96  INFLUENZA 

from  Portugal,  and  came  to  London  directly;  the  day  after  their  arrival 
the  lady,  two  servants  and  two  children  were  all  seized.  Two  men-of- 
war  arrived  at  Gravesend  from  the  West  Indies;  three  Custom-house 
officers  went  on  board;  a  few  hours  afterwards  the  crews  of  both  vessels 
were  attacked.  Some  other  cases  are  on  record  where  the  incubative 
period,  if  it  existed,  could  not  have  been  more  than  a  single  day.  On 
the  other  hand,  some  cases  are  on  record  in  which  the  incubative 
period  must  have  been  two  or  three  weeks." 

Leichtenstern  believed  that  the  usual  incubation  period  is  from 
one  to  three  days  although  some  cases  have  been  reported  in  which  it  is 
without  doubt  no  longer  than  twelve  hours.  Parsons  in  reporting 
for  England  also  gives  the  incubation  period  as  from  one  to  three  days 
as  a  rule. 

It  is  reported  in  France  in  1918  that  in  one  institution  thirty-one 
cases  out  of  thirty-three  individuals  occurred  within  three  days,  all  of 
them  infected  by  one  nurse. 

MacDonald  and  Lyth  report  in  the  British  Medical  Journal  for 
November,  1918,  an  interesting  observation  concerning  the  incubation 
period  in  influenza.  These  two  individuals  were  traveling  from  London 
to  York  in  the  same  compartment  with  an  individual  who  was  just 
convalescing  from  influenza.  Exactly  forty-one  hours  after  being  on 
the  train  with  this  individual,  they  both  came  down  with  the  disease. 
One  suffered  hghtly  while  the  other  was  severely  ill.  The  wife  and 
two  children  of  the  latter  contracted  the  disease  in  turn,  and  with 
them  also  the  first  symptoms  appeared  suddenly  after  a  delay  of 
about  forty-eight  hours. 

Stanley,  in  studying  the  epidemics  of  influenza  in  San  Quentin 
Prison,  found  that  as  a  rule  there  was  an  increase  in  incidence  follow- 
ing the  Sunday  picture  shows.  This  usually  occurred  on  Tuesdays 
and  Wednesdays,  giving  an  apparent  incubation  period  of  from 
thirty-six  to  sixty  hours.  He  tabulated  the  records  of  twenty-nine 
individuals  who  had  presumably  become  exposed  at  the  show  and 
found  that  the  incubation  period  averaged  about  forty-eight  hours. 

The  majority  of  observers  give  the  incubation  period  as  from 
twenty-four  hours  to  four  or  five  days,  most  often  two  or  three  days. 

Pkedisposing   Causes. 

Not  every  individual  acquires  influenza.  There  are  those  who 
assume  that  the  disease  is  so  wide  spread  that  every  individual  in  each 
community  attacked  has  been  actually  exposed  to  the  disease.  In 
that  case  there  must  be  a  certain  amount  of  natural  immunity  which 


AN    EPIDEMIOLOGIC    STUDY  97 

protects  around  sixty  to  eighty  per  cent,  of  most  populations  from  the 
disease.  The  other  extreme  would  be  that  every  exposed  individual 
falls  victim  to  the  disease  and  that  only  twenty  to  thirty  or  forty  per 
cent,  are  actually  exposed.  The  true  state  probably  lies  between 
these  two  extremes. 

Nevertheless  it  is  a  fact  that  some  individuals  naturally  insuscepti- 
ble to  the  disease  fall  victim  as  a  result  of  the  action  of  some  extraneous 
force,  something  which  lowers  their  resistance.  Raw  recruits  in  the 
army  camps  in  the  fall  of  1918  contracted  the  disease  in  much  greater 
proportion  than  did  the  hardened  soldiers.  Fatigue,  intercurrent 
illness,  environmental  changes  and  exposure  to  inclement  weather  may 
all  predispose  to  infection  in  the  individual.  Greenwood  found  that 
the  compulsory  rationing  of  food  in  England  during  the  war  was 
probably  not  a  predisposing  cause  of  infection.  The  incidence  of  the 
disease  in  the  South  Africa  Union  where  food  was  abundant  was  even 
higher  than  that  for  the  British  Isles.  Hamer  calls  attention  to  the 
fact  that  the  ages  of  highest  incidence  during  the  pandemic  were  those 
ages  in  which  the  diet  was  perhaps  more  restricted  than  in  other  ages. 
This,  however,  is  but  one  factor  and  cannot  be  accepted  as  conclusive. 

It  had  been  suggested  that  in  the  army  camps  in  the  United  States 
typhoid  vaccination  during  the  epidemic  predisposed  to  the  disease. 
The  similarity  of  the  symptoms  in  vaccine  reaction  and  in  influenza 
may  have  suggested  this.  V.  C.  Vaughan  has  investigated  this  possi- 
bility and  finds  that  those  organizations  in  which  anti-typhoid  vaccine 
was  discontinued  for  a  time  after  the  appearance  of  the  influenza 
suffered  quite  as  severely  as  those  which  submitted  to  vaccination. 

Other  predisposing  causes,  such  as  the  incidence  of  crowding  in  a 
household  and  the  sanitary  surroundings  of  the  individual  will  be 
discussed  later. 

Periodicity. 

The  phenomenon  of  occurrence  of  epidemic  influenza  in  many 
countries,  even  on  different  continents  almost  simultaneously  and 
often  without  any  clear-cut  progressive  spread  from  one  of  these  coun- 
tries to  another  raises  the  question  of  periodicity  in  influenza.  Is  this 
simultaneous  occurrence  due  to  some  mechanism  in  the  life  cycle  of  the 
influenza  virus  whereby  it  regularly  acquires  increased  invasiveness, 
no  matter  what  its  geographical  distribution,  or  is  it  merely  a  feature 
of  the  meteorologic  conditions  that  makes  the  epidemic  appear  to  be 
simultaneous  in  widely  scattered  communities? 

Influenza  characteristically  returns.     An  influenza  period  usually 


98  INFLUENZA 

comprises  from  three  to  five  years,  with  one  or  two  very  mild  epidemics 
at  the  beginning  which  may  frequently  be  overlooked,  then  of  wide 
pandemic  spread,  to  be  followed  by  endemic  recurrences  for  as  long  as 
two  or  three  years.  During  these  influenza  periods  the  intervals 
between  waves  are  frequently  so  nearly  equal  or  multiples  of  each 
other  as  to  force  the  question  of  a  periodic  law.  Not  only  thus,  but 
even  on  a  larger  scale  does  the  disease  appear  with  a  certain  uniform 
regularity.  The  great  epidemics  are  separated  frequently  by  inter- 
vals approximating  decades.  Stallybrass  calls  attention  to  the 
epidemic  years  in  England,  which  are  1789-90,  1802-03,  1830-32, 
1840-41,  1848-49  and  1851,  1854,  1869-70,  1879,  1890-91,  1898,  and 
1918-19.  With  the  exception  of  1854  all  of  these  dates  are  around  the 
end  of  a  decennium. 

Yet,  again,  in  the  successive  waves  of  an  individual  epidemic,  as 
has  been  pointed  out  by  Pearl,  there  is  very  roughly  some  periodicity. 

Are  these  admittedly  obvious  phenomena  fundamental  features  of 
the  life  cycle  of  the  influenza  virus,  or  are  they  incidental,  due  to 
extrinsic  causes,  changes  in  the  pabulum,  in  the  host  as  an  individual, 
or  in  the  host  as  a  community,  or  changes  in  climatic  conditions?  Is 
it  a  basic  feature  upon  which  we  must  build  our  conception  of  the 
epidemiology  of  epidemic  influenza,  or  is  it  more  a  feature  of  chance? 
The  evidence  to  date  is  conflicting  and  incomplete.  The  answer  Ues 
in  the  future. 

Periodicity  in  the  acute  infections  is  not  a  new  subject.  It  has 
been  discussed  in  various  other  diseases,  particularly  in-measles.  For 
many  years  epidemiologists  in  many  parts  of  the  world  have  reported 
the  observation  of  a  periodicity  in  epidemics  of  measles.  It  is  gener- 
ally regarded  as  an  estabHshed  fact  that  each  locaKty  suffers  from 
epidemic  waves  of  this  disease  and  that  the  period  is  somewhere  about 
two  years.  In  certain  relatively  small  locaHties  in  England .  where 
registration  statistics  have  been  kept  for  many  years  the  Health 
Officers  count  on  an  epidemic  every  two  years.  In  some  places  the 
epidemic  is  expected  to  fall  during  the  even  years,  while  in  others  it 
occurs  in  the  odd  years. 

Brownlee  has  been  one  of  the  foremost  investigators  in  the  periodi- 
city of  influenza,  but  since  his  communication  on  that  subject  was  very 
brief,  we  take  occasion  to  quote  first  from  his  article  on  the  periodicity 
of  measles,  thereby  gaining  a  more  comprehensive  knowledge  of  his 
theory,  and  at  the  same  time  becoming  able  to  compare  the  periodicity 
in  the  two  diseases. 

"The  common  explanation  of  the  periodicity  of  epidemics  of  chil- 


AN    EPIDEMIOLOGIC    STUDY  99 

dren's  diseases  is  that  the  susceptible  children  take  the  disease  in 
sufficient  numbers  to  limit  the  further  spread.  The  epidemic  thus 
dies  out  to  recur  when  a  further  sufficif^nt  nuinlx-r  of  susceptible 
children  have  accumulated.  This  is  quite  a  feasible  theory  and  cer- 
tainly explains  the  periodicity  of  epidemics.  The  forms  of  epidemic 
curve  which  arise  on  this  hypothesis  are  not  unlike  those  actually 
found,  the  differences  being  no  more  than  might  be  expected  between  a 
mathematical  form  based  on  a  hypothesis  and  the  natural  conditions 
to  which  the  hypothesis  is  only  an  approximation.  This  explanation, 
however,  must  fail  if  epidemics  of  different  periods  can  be  shown  to 
exist  in  the  same  town  at  the  same  time,  and  I  think  this  has  been 
shown.  In  London,  which  on  account  of  its  size  might  be  assumed 
deserving  of  special  treatment,  the  existence  of  periods  of  different 
length  have  been  demonstrated.  In  Edinburgh,  Glasgow,  and  Bir- 
mingham also  it  has  been  shown  that  epidemics  with  periods  in  the 
neighborhood  of  ninety-eight  weeks  and  one  hundred  and  ten  weeks 
intermix.  The  same  epidemicity  even  applies  to  districts  in  London. 
In  the  West  end  of  London  we  have  almost  a  replica  of  what  occurs  in 
Glasgow,  Birmingham  and  Edinburgh.  The  main  period  there  is  97 
weeks,  the  secondary  period  109.5  weeks.  In  the  South  of  London 
one  period  is  that  of  97  weeks,  but  almost  equally  prominent  is  that  of 
87  weeks.  The  whole  evidence,  therefore,  seems  to  point  to  some  con- 
dition in  the  organism  which  produces  the  disease  as  the  potent  cause 
of  the  difference  rather  than  to  the  number  of  susceptible  children. 
Compare  the  Paramoecium  which  under  natural  conditions  divides 
asexually  for  several  hundred  times  and  then  dies  out  unless  conju- 
gation takes  place.  The  resting  stage  following  conjugation  persists 
for  some  time. 

"There  is,  however,  one  point  of  great  importance  which  must  be 
considered.  If  an  epidemic  begin  in  a  definite  locality  and  spread 
from  that  locality,  and  if  there  is  no  loss  of  infectivity  on  the  part  of 
the  organism,  it  is  demonstrable  that  a  similar  proportion  of  the  popu- 
lation should  be  attacked  in  each  zone  as  the  epidemic  spreads  out- 
ward. On  the  other  hand,  if  the  organism  lose  the  power  of  infecting 
with  the  lapse  of  time,  in  each  additional  zone  invaded  the  proportion 
of  susceptible  persons  infected  should  become  smaller  and  smaller. 
Of  course  this  might  not  be  true  for  any  one  epidemic,  as  in  many 
parts  of  the  area  invaded  the  population  might  be  more  or  less  suscep- 
tible because  of  recent  attack  of  the  disease,  but  when  an  average  of 
twenty  outbreaks  has  been  taken  this  effect  should  be  eliminated,  the 
number  of  times  the  invading  organism  comes  into  contact  with  an 


100  INFLUENZA 

insusceptible  population  being  balanced  by  the  number  of  times  which 
it  meets  one  more  susceptible  than  the  average.  The  method  of 
spread  of  epidemics  on  the  average  should  thus  give  some  indication 
regarding  the  laws  which  determine  the  course  of  the  phenomenon. 
Now  with  regard  to  London,  the  clearest  facts  refer  to  the  87-weeks,  the 
97-weeks  and  the  109.5-weeks  period.  The  97-weeks  period  starts 
at  the  same  time  all  over  the  city  and  there  is  no  evidence  of  any 
special  center.  The  infection  seems  generalized.  With  regard  to  the 
87-weeks  epidemic,  however,  the  case  is  diiEferent.  This  seems  to 
start  in  St.  Saviour's  Parish  and  to  spread  thence  to  Camberwell, 
Lambeth,  etc.  In  this  epidemic  the  rate  of  spread  can  be  definitely 
measured.  The  maximum  occurs  later  and  later  as  the  distance  from 
the  center  is  increased  and  the  percentage  of  children  infected  is  also 
easily  observed  to  fall  as  the  time  increases.  With  regard  to  the  109.5- 
weeks'  period  epidemic  the  facts  are  similar  though  not  quite  so 
definite.  This  seems  to  show  that  for  at  least  two  strains  of  organisms 
the  epidemic  ceases  because  the  organism  has  lost  its  power  of  infecting. 
It  may  be  inferred  that  an  epidemic  ceases  because  the  organism 
varies  in  its  potency  to  cause  infection.  A  cycle  of  epidemics  now 
coinciding  and  now  differing  in  their  maxima  can  thus  be  explained. 
Some  kind  of  life  cycle  exists  in  the  infecting  organism.  In  this  life 
cycle  high  powers  of  infecting  are  attained  probably  after  a  resting 
state:  a  period  of  activity  follows  and  gives  place  to  a  period  of  rest; 
the  average  length  of  the  cycle  is  determined  by  the  strain  of  the 
organism." 

There  are  certain  drawbacks  to  Brownlee's  work  and  conclusions. 
We  quote  from  V.  C.  Vaughan,  who  has  discussed  Brownlee's  work, 
not  only  because  of  his  good  summary  of  the  difficulties  and  disad- 
vantages of  the  method,  but  particularly  because  the  same  dis- 
advantages and  possibility  of  inaccurate  conclusions  hold  in  the  case 
of  influenza. 

''There  is  no  reason  for  supposing  that  the  virus  of  measles  is  con- 
trolled in  any  way  by  our  calendar.  In  order  to  get  anywhere  in 
determining  any  law  of  periodicity  in  epidemics  we  must  know  the 
morbidity  and  mortality  of  the  disease  by  days,  or  at  least  by  weeks. 
In  different  parts  of  a  large  city  there  may  be,  and  undoubtedly  are, 
epidemic  waves  of  measles  on  the  flow  or  on  the  ebb  at  the  same  time. 
The  best  work  that  has  been  done  along  this  line  is  that  of  Brownlee, 
who  has  figured  out  epidemic  waves  of  measles,  based  on  the  weekly 
numbers  of  deaths  in  London  between  1840  and  1912. 

"The  figures  presented  by  Brownlee  are  of  great  value,  and  his 


AX    Kl'IDEMIOLOGIC    STUDY  101 

theory  is  fascinating  and  has  mucli  in  its  favor,  not  onl}-  in  a  study  of 
epidemics  of  measles,  but  of  the  other  infectious  diseases  of  infancy 
and  childhood,  especially  scarlet  fever,  whooping-cough,  and  chicken- 
pox.  In  order  to  solve  the  problem  of  periodicity  in  measles  we  nmst 
have  more  exact  information  than  we  now  possess.  Brownlee's 
figures  pertain  to  deaths  onlj\  There  are,  so  far  as  we  know,  n:)where 
in  the  world  satisfactory  statistics  concerning  morbidity  in  this  disease. 
Deaths  from  measles  are  so  largely  determined  by  the  care  bestowed 
upon  the  sick  and  upon  the  extent  to  which  secondary  infection  is 
prevented  that  we  are  inclined  to  hesitate  about  the  acceptance  of 
a  death  rate  or  number  of  deaths  from  this  disease  as  an  index  to  the 
virulence  of  the  organism  causing  the  disease;  in  other  words,  we  are 
not  convinced  that  the  death  rate  in  a  given  outbreak  of  this  disease 
is  a  measure  of  the  virulence  of  the  organism  causing  it.  This  involves 
the  question  whether  measles  per  se  is  a  disease  of  wide  variation  in 
malignancy  or  are  the  widely  different  death  rates  observed  in  different 
epidemics  due  to  secondary  infections.  The  streptococcus,  a  common 
invader  of  the  body  during  the  progress  of  a  measles  infection,  is  known 
to  possess  a  most  variable  degree  of  malignancy.  We  are  inclined  to 
the  opinion  that  if  all  cases  of  measles  could  be  recognized  before 
secondary  infection  occurs  and  could  be  cared  for  ideally  the  death 
rate  from  this  disease  in  different  epidemics  would  be  much  more 
uniform  than  is  now  shown  and  w^ould  be  low.  The  greatest  danger 
to  life  in  an  attack  of  measles  lies  in  the  fact  that  the  virus  lowers  the 
resistance  of  the  body  cells  and  opens  gateways  to  more  deadly  or- 
ganisms, such  as  the  streptococcus.  We  believe  that  there  are 
demonstrated  facts  which  support  these  ideas.  Quite  uniformlj^  in 
measles  there  is  a  well  marked  leukopenia.  As  we  now  interpret  it, 
this  means  a  decrease  in  the  number  of  the  forces  that  naturally  protect 
the  body  against  the  invasion  of  foreign  cells.  Again  as  we  interpret 
it,  the  failure  of  the  body  cells  to  respond  to  the  tuberculin  test  during 
a  course  of  measles  or  soon  thereafter  is  evidence  that  the  resistance 
of  the  body  is  lowered.  If  our  interpretation  on  these  points  be 
correct  we  fail  to  see  how  deaths  from  measles  can  be  properly  em- 
ployed as  a  standard  in  the  measurement  of  the  virulence  of  the 
organism  of  the  disease." 

Recognizing  then  the  obvious  disadvantages  of  the  method,  we  will 
turn  to  the  work  done  on  periodicity  in  influenza.  We  should  call 
attention  at  this  point  to  the  fact  that  the  establishment  of  periodicity 
would  carry  with  it  the  assumption  that  the  third  of  our  three  hy- 
potheses concerning  the  origin  of  influenza  is  the  correct  one.     For 


102  INFLUENZA 

example,  the  July  and  autumn  epidemic  in  England,  as  well  as  all 
occurring  subsequent  to  them,  would  be  due  to  a  virus  or  several 
viruses  which  have  been  endemic  in  England  since  1889,  in  fact  since 
man  has  been  in  England,  and  the  epidemics  and  their  recurrences 
would  be  due  to  increase  in  the  virulence  of  this  local  virus.  The  virus 
is  distributed  over  the  earth  and  may  become  virulent  periodically 
in  many  countries  at  the  same  time,  or  if  the  periodicity  is  different 
on  two  continents  the  epidemics  would  occur  at  different  times. 

Periodicity  is  not  a  new  hypothesis.  Hirsch  denied  any  periodicity 
distinct  enough  to  be  revealed  by  the  comparatively  crude  statistical 
methods  of  his  time.  Periodicity  if  present  can  only  be  revealed  by 
detailed  and  compUcated  mathematical  procedures.  Brownlee  has 
investigated  the  weekly  number  of  deaths  from  influenza  in  London 
between  1889  and  1896,  and  also  up  to  the  present  time.  He  has 
compared  these  with  the  weekly  number  of  deaths  from  bronchitis 
and  pneumonia  in  London,  the  records  of  which  have  been  available 
since  1870.  By  the  method  of  the  periodogram  he  showed  that  there 
was  a  regular  periodicity  of  33  weeks  in  deaths  from  influenza  between 
the  years  1889  and  1896,  but  that  in  later  years  there  was  some  con- 
siderable aberration.  He  concluded  that  for  some  reason  influenza 
periods  tend  to  recur  at  33-week  intervals  after  the  primary  epidemic, 
and  that  the  favorable  season  for  its  recurrence  is  from  January  to  the 
end  of  May.  Should  the  33d  week  fall  in  other  than  these  winter 
months  the  epidemic  may  be  mild  or  even  missed,  appearing  after 
another  33-week  interval.  Epidemic  influenza  does  not  assume  a  form 
which  causes  any  large  number  of  deaths  until  a  bronchitic  or  pneu- 
monic constitution  has  been  established.  The  fatal  form  is  usually  a 
disease  of  the  winter  or  spring.  He  also  found  that  in  the  absence  of 
influenza,  bronchitis  and  pneumonia  did  not  show  a  33-week  periodi- 
city, but  when  associated  with  influenza  these  conditions  also  became 
periodic  (33  weeks),  and  he  assumes  that  this  change  is  definitely 
associated  with  the  appearance  of  influenza. 

Between  1876  and  1890  there  was  no  tendency  to  the  33-week 
periodicity  with  regard  to  bronchitis  and  pneumonia,  but  it  was  very 
marked  between  1889  and  1896.  During  this  epidemic  period  the 
deaths  from  pneumonia  precede  those  from  influenza  by  one  week  and 
those  of  bronchitis  precede  those  of  influenza  by  two  weeks.  The 
number  of  deaths  from  bronchitis  and  pneumonia  ascertained  by  this 
method  of  grouping  is  fully  twice  the  number  obtained  from  influenza 
alone. 


AN    EPIDEMIOLOGIC    STUDV  103 

He  believes  that  in  these  years,  influenza  appeared,  on  its  epidemic 
onset,  first  with  bronchitic  symptoms,  later  with  pneumonic  symptoms, 
and  lastly  with  those  symptoms  more  definitely  associated  with  influ- 
enza proper.  When  the  several  sets  of  deaths  are  added  together  in 
33-week  periods  a  very  typical  epidemic  makes  its  appearance. 

Brownlee  finds  that  in  the  monthly  statistics  of  Glasgow,  Aberdeen, 
Massachusetts,  etc.,  there  has  been  nothing  differing  essentially  from 
this  phenomenon  found  in  London. 

Between  1876  and  1889  the  annual  curve  for  bronchitis  and  pneu- 
monia shows  two  maxima,  one  at  the  end  of  January  and  the  second 
in  the  middle  of  March.  From  March  the  decline  in  deaths  from 
bronchitis  is  very  rapid.  The  disease  re-appears  around  the  beginning 
of  October.  During  the  period  1889-96  the  maximum  number  of 
deaths  from  bronchitis  occurred  in  the  second  week  of  January  and  the 
last  week  of  February.  Both  of  these  maxima  are  a  fortnight  before 
the  maxima  of  the  epidemics  of  influenza.  This  suggests  that  the 
advent  of  influenza  has  brought  a  change  in  the  seasonal  prevalence  of 
bronchitis  and  supports  the  view  that  the  earUer  portion  of  the  influ- 
enza epidemic  is  associated  wdth  bronchitic  symptoms.  The  same 
phenomenon  holds  for  pneumonia. 

Brownlee  was  able  to  predict  correctly  the  date  of  the  recent  1920 
epidemic.  He  did  not  attempt,  however,  to  explain  the  short  interval 
between  the  summer  and  autumn,  1918,  epidemics  in  England.  He 
speaks  of  the  second  as  "aberrant."  In  other  words,  it  does  not  fall 
within  his  classification.  October  is  not  a  high  respiratory  disease 
month.     The  epidemic  should  have  been  mild. 

Stallybrass  has  confirmed  Brownlee's  33-week  periodicity  and  sug- 
gests an  explanation  for  the  "aberrant"  October  epidemic.  Using 
periodograms  with  a  33-week  basis,  and  plotting  deaths  from  influenza 
and  respiratory  diseases  from  January,  1890,  through  January',  1920, 
he  finds  that  the  most  definite  33-week  periodicity  is  shown  during  the 
years  1890-99.  During  this  period  there  is  one  maximum,  when  all 
33-week  periods  are  superimposed,  which  occurs  at  the  seventh  week 
of  the  cycle.  Beginning  about  1899  a  new  maximum  appears  in  the 
nineteenth  week  of  the  cycle,  which  continues  to  recur  untU  the 
culminating  point  is  reached  in  the  week  ending  October  26,  1918. 
An  additional  66  weeks  carries  the  date  forward  to  the  first  week  in 
February,  1920.  The  maximum  at  the  seventh  week  of  the  periodo- 
gram  during  the  years  1899-1913  is  greatly  diminished  from  that  in 
1890  -98.  The  periodogram  for  1914-1919  shows  clearly  both  maxima, 
that  in  the  seventh  and  that  in  the  nineteenth  weeks. 


104  INFLUENZA 

We  quote  Stallybrass  in  some  detail  (see  Chart  XII) : 

''Dr.  John  Brownlee  pointed  out  that  from  July  13th  to  March  1st 
(the  maxima  of  the  summer  wave  of  1918  and  of  the  spring  wave  of 
1919)  is  33  weeks,  but  that  the  wave  having  its  crest  in  this  country 
on  November  2,  1918,  does  not  fall  into  the  sequence,  leaving  one  to 
infer  that  there  were  two  strains  of  the  influenzal  virus  in  operation. 

''I  supplement  his  investigation  by  the  weekly  deaths  occurring  in 
Liverpool  during  the  period  1890-1919  that  were  ascribed  to  influenza 
and  to  all  respiratory  diseases.  Prior  to  1890  there  were  no  deaths 
attributed  to  influenza  for  a  number  of  years. 

"Closely  corresponding  with  Brownlee's  observations  on  London 
by  far  the  most  definite  periodicity  is  shown  during  the  years  1890- 
1899,  during  which  period  there  is  one  well-marked  maximumy  at  the 
seventh  week  of  the  cycle.  During  the  period  1899-1913  a  new  maxi- 
mum in  the  nineteenth  week  of  the  cycle  comes  into  play  and  continues 
to  recur  until  the  culminating  point  is  reached  in  the  week  ending 
October  26,  1918,  a  week  earlier  than  in  most  English  towns  (Wave 
III) ;  a  further  66  weeks  carries  one  forward  to  the  first  week  in  Febru- 
ary of  this  year,  as  Brownlee  pointed  out,  and  the  outbreaks  that 
are  being  reported  in  Japan,  Paris,  Chicago,  New  York,  etc.,  would 
show  that  this  strain  has  punctually  reappeared. 

"There  is  also  evidence  in  the  table  of  a  small  maximum  at  the 
twenty-seventh  week  of  the  cycle  in  the  earlier  sub-period,  and  at 
the  twenty-ninth  week  in  the  later  sub-period ;  slight  movements  of  the 
maxima  forwards  or  backwards  in  the  cycle  over  .a  number  of  years 
may;  perhaps,  indicate  a  periodicity  slightly  greater  or  less  than  33 
weeks.  The  twenty-ninth  week  of  the  cycle  fell  on  the  weeks  ending 
May  18,  1918,  and  January  10,  1919.  An  examination  of  the  figures 
in  Dr.  Hope's  annual  report  for  Liverpool  for  1918  shows  that  there 
was  a  definite  wave  of  influenza  reaching  its  crest  on  May  18th  (Wave 
I),  and  there  is  also  a  definite  rise  in  the  deaths  from  influenza,  respi- 
ratory diseases,  and  from  all  causes,  making  a  small  peak  in  the  week 
ending  January  3,  1919,  but  it  is  hidden  by  the  enormous  waves  of 
October  and  March,  so  that  it  only  appears  as  an  irregularity  in  the 
curve;  but  it  was  noted  at  the  time  that  influenza  had  not  declined 
in  Liverpool  in  January  in  the  way  that  it  had  in  practically  all  other 
English  towns.  These  two  waves  do  not  appear  to  have  played  a 
large  part  in  this  country,  but  the  outbreaks  in  the  Grand  Fleet  in 
May,  1918,  and  also  in  Spain,  Glasgow,  etc.,  may,  perhaps,  be  attrib- 
uted to  it.  In  the  United  States  in  January,  1919,  it  would  appear 
to  have  played  a  much  larger  part.     In  a  large  number  of  American 


CHART  XII. 


Periodogram  based  on  the  weekly  influenza  deaths  in  Liverpool  between  1890 
and  1919.     The  curves  are  based  on  a  thirty-three  week  periodicity.     (Stallyhrass.) 


AX    EPIDEMIOLOGIC    STUDY  105 

cities  two  waves  are  experienced,  the  first  being  the  October  wave; 
the  crest  of  the  second  wave  sometimes  fell  in  March,  as  did  one  of  the 
crests  in  this  country,  but  in  a  number  of  instances,  e.g.,  Cambridge, 
Washington,  San  Francisco,  New  Orleans,  etc.,  it  fell  in  January,  or  to 
be  exact,  in  the  thirty-first  and  thirty-second  weeks  of  the  cycle. 
The  close  relationship  of  Liverpool  and  Glasgow  with  the  United  States 
through  the  incoming  stream  of  American  troops  may  perhaps  account 
for  the  presence  of  this  May  wave  in  these  two  towns,  and  not  the 
rest  of  England. 

"The  third  maximum  in  the  fourth  week  of  the  cycle  is  represented 
during  the  late  outbreak  bj'  the  waves  culminating  in  Liverpool,  and 
also  the  greater  number  of  English  towns  on  the  weeks  ending  July 
13  (Wave  II)  and  March  1  (Wave  IV).  This  is  a  33-week  interval. 
This  wave  recurred  at  an  interval  of  32-34  weeks  in  a  large  number  of 
English  towns. 

"Of  65  towns  which  experienced  all  three  waves  47  (72  per  cent.) 
had  their  maxima  in  the  summer  and  spring  epidemics  within  an 
interval  of  32-34  weeks ;  but  comparing  the  week  in  which  any  given 
town  had  its  epidemic  peak  in  the  summer  and  autumn,  and  autumn 
and  spring  epidemics  onl}^  27  (41  per  cent.)  and  31  (47  per  cent.) 
respective!}^  fell  within  the  Limit  of  a  week  on  either  side.  The  time 
relationships  of  the  maxima  in  summer  and  spring  were  much  closer 
to  each  other  than  they  were  to  the  autumn  maxima. 

'Tf  it  should  prove  correct  that  there  were  three  strains  of  the 
influenzal  \'irus,  each  with  a  periodicity  of  about  33  weeks,  and  that 
simultaneously  all  three  strains  became  enhanced  in  both  virulence 
and  infecti\aty,  then  we  are  faced  with  a  phenomenon  without  an 
exact  parallel,  although  the  behavior  of  the  meningococcal  \aruses 
during  the  war  presents  some  points  of  similarity.  So  far  the  weight 
of  evidence  leans  to  such  an  exaltation  of  a  widespread  endemic  strain 
or  strains  rather  than  to  dissemination  from  any  particular  focus  in 
the  world.  In  any  case  doubtless  a  good  deal  of  spread  of  infection 
took  place." 

Spear  takes  exception  to  the  work  of  Brownlee  and  Stallybrass,  and 
points  out  that  the  periodogram  is  not  applicable  to  the  study  of 
recurrent  epidemics  unless  the  recurring  waves  are  of  approximately 
uniform  "amplitude. "  In  that  case  nothing  could  be  less  appropriate 
for  this  study  than  the  influenza  waves  which  vary  from  very  small  to 
extremely  high,  as  in  1918. 

Spear  describes  two  simple  tests  which  he  applied  to  demonstrate 
the  existence  or  non-existence  of  periodicity. 

9 


106  INFLUENZA 

First  he  divided  each  of  the  last  thirty  years  into  13  four-weekly 
periods,  and  tabulated  the  frequency  with  which  the  observed  week  of 
maximum  mortahty  falls  into  one  or  other  of  the  13  groups.  He 
discovered  that  the  climax  of  an  influenza  prevalence  falls  more 
frequently  in  the  second  and  third  four-weekly  period  than  in  others — 
i.e.,  the  moaths  of  February  and  March.  Had  there  been  a  33-week 
periodicity  there  would  have  been  an  equal  number  of  these  climaxes 
in  each  of  the  13  divisions  of  the  year. 

Brownlee,  according  to  Spear,  was  correct  in  his  prediction  that 
influenza  would  occur  in  February,  1920,  for  the  reason  that  January 
or  February  is  the  most  likely  time  for  an  influenza  prevalence  in  any 
year. 

Spear's  second  test  of  periodicity  consisted  in  plotting  the  inter- 
epidemic  periods  according  to  the  number  of  weeks  intervening.  Were 
there  a  33-week  periodicity,  he  says,  that  nearly  all  interepidemic 
periods  should  fall  in  this  group.  As  a  matter  of  fact,  more  than  twice 
as  many  periods  fall  in  the  42-58  weeks  interval  than  in  any  other 
interval.  Fifteen  fall  within  this  period,  six  in  the  period  59-75  weeks, 
five  in  the  period  8-24  weeks,  and  only  four  in  the  period  25-41  weeks. 
There  was  one  in  the  period  76-92  and  one  110  plus.  Finally  in  the 
thirty  years  1890-1919  there  were  thirty-two  climaxes  or  peaks  in  the 
"influenza"  mortality. 

Spear  concludes  that  if  there  is  any  periodicity  it  is  around  fifty 
weeks,  or  a  year. 

The  fallacy  in  the  work  of  Stallybrass  and  of  Brownlee,  according 
to  him,  is  that  the  mortahty  in  the  third  week  of  1892,  the  twentieth 
week  of  1891,  and  the  tenth  week  of  1895,  and  in  the  big  epidemic  of 
1918  so  overshadowed  all  the  other  peaks  that  the  smaller  ones  became 
lost  in  these  larger  waves. 

Brownlee  does  not  claim  a  33-week  periodicity  during  interepi- 
demic periods.     This  part  of  Spear's  criticism  is  not  valid. 

Vaughan's  objections  to  the  conclusions  on  measles  hold  equally 
well  with  regard  to  influenza.  Finally,  we  must  remember  that  in 
parts,  at  least,  of  the  work  of  Brownlee  and  Stallybrass,  they  are  not 
studying  chiefly  influenza  deaths,  but  deaths  reported  as  due  to 
bronchitis  and  pneumonia. 

After  a  study  of  the  pros  and  cons  of  the  question  of  periodicity 
the  author  submits  by  way  of  summary  his  conclusions: 

1.  Influenza  does  tend  to  recur  at  intervals.  It  has  not  been 
proven  that  these  intervals  are  always  of  equal  length. 

2.  At  the  present  the  opinions  concerning  the  periods  are  diver- 


AN   EPIDEMIOLOGIC    STUDY  107 

gent.  We  have  the  33-week  periodicity  of  Brownlee  and  Stallybrass, 
the  one-year  period  of  Spear,  the  seven-week  intervals  suggested  by 
Pearl,  and  the  apparent  twelve-week  recurrences  in  England  in  1918 
and  1919. 

3.  It  is  to  be  noted  that  particularly  in  the  work  of  Stallybrass,  in 
order  to  prove  his  periodicity,  he  finds  it  necessary  at  times  to  quote 
epidemics  occurring,  not  in  England,  but  in  fairly  remote  parts  of  the 
world,  as  in  the  United  States  and  Japan.  We  have  shown  that  in  the 
interval  between  1918  and  1920  an  epidemic  could  be  discovered 
somewhere  on  the  earth  in  many  months,  perhaps  even  in  every 
month  during  this  interval.  It  is  to  be  regretted  that  following  the 
criticism  by  Spear  there  has  been  no  further  report,  so  far  as  we  know, 
by  either  Brownlee  or  Stallybrass. 

4.  It  is  quite  possible,  even  probable,  that  influenza  is  endemic  in 
mild  form  throughout  the  inter-pandemic  years  in  England,  as  well  as 
in  many,  or  all  other  countries,  but  it  is  equally  possible  or  probable 
that  the  particular  virus  which  gave  rise  to  the  pandemic  was  not  one 
which  simultaneously  increased  in  virulence  in  all  countries,  but  was 
one  which  had  its  origin  in  one  comparatively  well  localized  focus. 

5.  Our  own  theory  does  not  explain  the  autumn  recurrence  in  1918 
in  England,  following  that  of  May,  June  and  July.  We  have  traced 
the  original  spread  to  England  and  have  left  it  at  that  point.  We 
have  again  taken  it  up  in  the  autumn  when  it  became  severe,  and  was 
returned  to  the  United  States.  The  interval  of  quiescence  in  England 
and  elsewhere  may  need  further  explanation.  Two  alternative 
hypotheses  suggest  themselves:  First,  that  the  autumn  recrudescence 
is  entirely  comparable  to  later  ones,  and  is  but  a  manifestation  of  the 
characteristic  feature  of  recurrence  in  influenza.  Had  the  autumn 
epidemic  been  mild  and  had  it  not  so  overshadowed  all  others,  we 
would  have  classified  it  with  those  of  early  1919  as  being  merely 
recrudescences  of  the  summer  spread.  Evidence,  particularly  in 
favor  of  this,  is  the  report  of  Greenwood  previously  mentioned  which 
shows  that  in  England  the  autumn  spread  partook  of  the  nature  of  a 
secondary  type  of  epidemic,  as  compared  with  the  primary  type  in 
the  summer. 

The  second  hypothesis  is  that  the  occurrence  in  the  summer  in 
England  of  an  epidemic  due  to  a  virus  imported  from  America  or 
France  or  China,  with  its  consequent  increase  in  morbidity,  so 
enhanced  the  virulence  of  a  local  endemic  British  virus  that  the  latter 
produced  the  autumn  epidemic.  We  see  no  necessity  for  complicating 
the  question  by  the  assumption  of  this  second  hypothesis. 


108  INFLUENZA 

6.  Whether  or  not  there  is  a  regular  periodicity  of  a  definite 
number  of  weeks  in  the  case  of  influenza,  the  fact  remains  beyond 
cavil  that  one  of  the  dominant  characteristics  of  epidemic  influenza 
is  its  recurrence  at  intervals.  The  evidence  is  ample  that  the  disease 
is  distributed  throughout  many  countries  in  inter-epidemic  times  and 
that  intermittent  outbreaks  of  large  or  small  extent  occur. 

The  most  striking  phenomenon  is  the  fact  that  in  March  of  1918 
influenza  is  reported  as  having  been  present  in  China,  in  the  United 
States  and  in  France.  It  is  scarcely  possible  that  the  disease  in  its 
epidemic  form  could  have  been  carried  from  any  one  of  these  three 
points  to  the  other  two  in  the  remarkably  short  time  between  the 
onset  of  the  three  outbreaks.  We  are  faced  with  the  phenomenon  of  a 
simultaneous  exaltation  of  the  influenza  virus  in  three  remotely 
separated  countries  of  the  world.  This  one  fact  more  than  any  other 
indicates  that  the  fluctuation  in  virulence  is  dependent  upon  some 
factor  intrinsic  in  the  virus  itself  and  not  upon  environmental  factors. 

It  is  impossible  at  the  present  time  to  decide  whether  the  world 
epidemic  spread  simultaneously  from  these  three  foci  or  whether  in 
only  one  of  these  three  the  virus  became  so  exalted  as  to  produce 
pandemic  prevalence.  All  we  can  say  is  that  we  are  able  to  trace 
consecutively  the  spread  of  the  influenza  from  the  focus  in  the  United 
States  throughout  the  world.  The  information  upon  which  we  base 
our  findings  is  not  statistical,  and  as  we  have  previously  said  this 
latter  type  of  demographic  study  should  be  brought  into  use  to  either 
corroborate  or  disprove  our  findings. 

Virulence  Enhancement. 

Before  attempting  to  study  the  mechanism  of  origin  of  the  1918 
pandemic  it  is  highly  essential  that  we  devote  some  attention  to  a 
consideration  of  the  processes  by  which  the  germs  of  infection,  particu- 
larly the  virus  of  influenza,  may  develop  an  increase  in  virulence. 
Followers  of  the  theory  of  periodicity  would  base  virulence  enhance- 
ment primarily  on  some  intrinsic  property  of  the  virus  itself.  We 
know  from  past  experience  and  particularly  from  animal  experiments 
that  this  is  not  the  only  manner  by  which  virulence  may  be  increased. 

As  far  as  we  know  there  is  no  new  infectious  disease.  Individuals 
who  delve  into  the  history  of  the  past  inform  us  of  more  and  more 
diseases  which  were  well  known  to  the  ancients.  We  are  frequently 
amazed  at  the  variety  of  diseases  now  known  to  be  infectious  that  were 
very  correctly  described  by  the  Hippocratic  writers.  The  infectious 
diseases  are  with  us  always  and  live  nearly  always  in  man,  the  host 


AN    EPIDEMIOLOGIC    STUDY  109 

There  are  few  exceptions.  Very  few  of  the  contagious  viruses  can 
live  for  any  long  period  of  time  outside  of  the  human  body.  A  few, 
such  as  the  plague  bacillus^  may  live  on  other  hosts,  but  these  are  the 
exception.  The  remarkable  feature  is  that  for  long  periods  of  time 
the  virus  exists  in  the  host  in  a  quiescent  state  and  only  at  intervals 
does  it  become  highly  invasive  and  thereby  produces  epidemics  of 
greater  or  less  extent.  Under  what  conditions  does  the  metamorpho- 
sis of  the  microorganisms  occur? 

Topley,  in  the  Goulstonian  lectures,  discusses  this  subject.  He 
says:  "The  first  difficulty  with  which  we  were  faced  in  forming  any 
theory  of  the  spread  of  bacterial  infection,  which  should  conform  to 
the  known  facts  of  epidemiology,  was  to  find  some  explanation  of  the 
perpetuation  of  the  virus  during  interepidemic  periods.  The  bacter- 
iologic  data  w^hich  have  accumulated,  especially  during  the  last  twenty 
years,  have  shown  that  the  causative  agents  of  specific  diseases  are  to 
be  found  in  apparently  normal  persons  who  give  no  history  of  having 
been  in  contact  with  the  disease  in  question,  as  well  as  in  contact  with 
actual  cases  of  the  disease.  Moreover,  the  organisms  in  question 
have  been  shown,  in  certain  cases,  to  persist  for  long  periods  of  time 
in  or  upon  the  tissues  of  their  hosts,  and  we  must  always  remember  that 
the  difficulty  of  bacteriologic  technic  is  likely  to  lead  to  a  serious 
under-estimate.  Clinical  and  epidemiologic  investigations  have 
yielded  confirmatory  evidence,  and  we  are  thus  left  with  a  conception 
of  the  virus  of  a  given  disease  being  distributed  fairly  widely  through- 
out the  world  as  an  apparently  harmless  parasite  on  the  human  host, 
but  taking  on  during  epidemic  periods  a  new  and  sinister  role,  only  to 
relapse  again  into  comparative  quiescence  as  the  epidemic  subsides." 

He  explains  the  rise  of  the  epidemic  wave  as  follows:  "There  are 
at  least  three  possi*ble  explanations — an  increase  in  the  power  of  the 
parasite  to  produce  disease,  a  decrease  in  the  resistance  of  the  host, 
and  some  attraction  in  the  surrounding  circumstances  which  favor  the 
transference  of  parasites  from  case  to  case  without  any  alteration  of 
the  pathogenicity  of  the  one  or  in  the  resistance  of  the  other.  The 
third  of  these  hypotheses  may,  I  think,  be  disregarded.  That  altera- 
tions in  environment  may  be  the  determining  cause  in  initiating  an 
outbreak  of  bacterial  disease  is  probable  enough;  but  they  will  almost 
certainly  act  through  the  variations  which  they  bring  about  in  the 
other  two  factors.  The  whole  of  bacteriologic  knowledge  is  clearly 
against  the  occurrence  of  a  considerable  epidemic  in  which  the  patho- 
genicity of  the  parasite  and  the  resistance  of  the  host  remain  constant. 
Again,  while  we  may  well  beheve  a  lowered  resistance  of  a  certain 


110  INFLUENZA 

number  of  the  host-species  to  be  an  important  factor  in  the  initia- 
tion of  the  process,  yet  we  cannot  believe  that  it  is  the  whole  story. 
The  widespread  ravages  of  many  epidemics  would  seem  altogether  to 
preclude  such  an  explanation.  We  seem  forced  therefore  to  the  con- 
clusion that  an  increase  in  the  pathogenicity  of  the  specific  parasite 
is  an  essential  factor  in  the  rise  of  epidemics,  excluding  from  this 
category  small  sporadic  outbreaks  which  may  be  due  to  the  introduc- 
tion of  a  fully  virulent  parasite  by  a  healthy  carrier  in  some  other  way." 
If  a  disease  Hke  measles  is  quiescent  in  a  given  community  it  must 
be  that  in  that  locaHty  the  hosts  and  parasites  are  existing  in  a  state  of 
biological  equihbrium.  They  are  hving  in  a  state  somewhat  akin  to 
symbiosis.  Such  a  condition  could  be  attained  either  by  a  diminution 
of  the  invasive  powers  of  the  parasite,  or  by  an  increase  in  resistance 
of  the  host.  Probably  both  elements  are  active;  as  the  relative  im- 
munity of  the  host  rises  the  infectivity  or  virulence  of  the  parasite 
must  rise  to  an  equal  extent  to  maintain  the  equihbrium.  If  this  were 
true  we  would  find  that  in  those  locahties  in  which  the  disease  is  ende- 
mic and  where  the  population  is  relatively  resistant  there  is  a  normally 
more  virulent  virus  in  existence.  A  stranger  coming  into  such  a 
community  would,  in  view  of  his  lower  resistance  to  the  virus,  be 
more  susceptible  of  becoming  actively  infected.  There  would,  how- 
ever, be  httle  danger  of  an  epidemic  spead  because  the  number  of 
susceptibles  would,  roughly,  be  hmited  to  the  number  of  strangers 
in  the  community.  If,  however,  an  individual  from  the  community 
carrying  the  more  virulent  virus  were  to  travel  to  another  community 
where  the  greater  proportion  of  the  population  was  relatively  less 
immune  the  field  would  be  fertile  for  the  beginning  of  an  epidemic. 
Furthermore,  there  is  the  possibihty  of  an  outbreak  in  the  first  com- 
munity if  there  should  occur  gross  changes  in  its  constitution;  another 
infectious  disease,  a  redistribution  of  the  population  with  greater 
crowding,  anything  to  change  the  balance  between  host  and  parasite. 
Theobald  Smith  has  described  this  possibility  very  clearly : 
''During  the  ehmination  of  the  more  virulent  races  of  microorgan- 
isms, there  goes  on  as  weU  a  gradual  weeding  out  of  the  most  susceptible 
hosts.  In  a  state  of  nature  in  which  medical  science  plays  no  part, 
there  must  occur  a  shght  rise  in  the  resistance  of  individuals,  due  to 
selection  and  perhaps  acquired  immunity,  which  meets  the  decline 
of  virulence  on  the  part  of  microbes  until  a  certain  norm  or  equilibrium 
between  the  two  has  been  established.  The  equihbrium  is  different 
for  every  different  species  of  microorganism,  and  is  disturbed  by  any 
changes  affecting  the  condition  of  the  host  or  the  means  of  transmission 


AN    EPIDEMIOLOGIC    STUDY  HI 

of  the  parasite.  One  result  of  the  operation  of  this  law  is  the  low 
mortality  of  endemic  as  compared  with  epidemic  diseases.  Certain 
animal  diseases  while  confined  to  the  enzootic  territory,  cause  only 
occasional,  sporadic  disease,  but  as  soon  as  they  are  carried  beyond 
this  territory  epizootics  of  high  mortality  may  result.  Climate  in 
some  cases  enters  as  an  important  factor,  but  the  most  important, 
perhaps,  is  the  slight  elevation  in  virulence  brought  about  by  a  more 
highly  resistant  host.  The  most  susceptible  animals  are  weeded  out 
and  the  rest  strengthened  by  non-fatal  attacks.  The  virulence  of  the 
microbe  rises  slightly  to  maintain  the  equilibrium.  In  passing  into 
a  hitherto  unmolested  territory,  the  disease  rises  to  the  level  of  an 
epizootic  until  an  equilibrium  has  been  established. 

"The  same  is  true  of  human  diseases,  among  which  smallpox  is  a 
conspicuous  example.  The  great  pandemics  of  influenza,  which  seem 
to  travel  from  east  to  west  every  one  or  two  decades,  soon  give 
away  to  sporadic  cases,  and  the  careful  work  of  many  bacteriologists 
would  indicate  that  the  influenza  bacilli  found  at  present  have  fallen 
to  the  level  of  secondary  invaders,  and  are  parasites  of  the  respiratory 
tract  in  many  affections." 

Smith  describes  his  hypothesis  that  the  tendency  of  microbes  in 
perfecting  the  parasitic  habit  is  to  act  solely  on  the  defensive.  The 
aim  of  microorganisms,  if  we  may  speak  of  such,  is  to  become  able  to 
live  unharmed  on  the  host.  If  they  kill  the  host  they  have  lost  their 
home.  The  biologic  tendency  would  be  in  this  case  for  diseases  which 
were  once  acute  to  become  more  and  more  chronic  and  indolent. 

The  extremely  virulent  parasite,  which  kills  its  host,  will  die 
with  the  host  unless  it  has  effected  a  means  of  exit  before  its  death 
and  escapes  into  a  new  host.  For  this  reason  Pasteur  failed  to  ex- 
terminate the  rabbits  of  Australia.  He  believed  that  with  races  of 
the  bacillus  of  rabbit  septicefnia,  which  were  very  virulent,  and  which 
destroj^ed  life  very  quickly,  all  that  would  be  necessary  was  to  start 
the  disease  among  the  rabbits  of  Australia  and  that  it  would  tend  to 
spread  and  would  kill  off  all  of  the  rabbits.  But  the  parasite  killed 
the  animals  before  it  had  perfected  for  itself  a  means  of  escape  from 
the  body  and  thereupon  died. 

"From  the  biologic  standpoint  which  I  have  endeavored  to  present, 
we  may  conceive  of  all  highly  pathogenic  bacteria  as  incompletely 
adapted  parasites,  or  parasites  which  have  escaped  from  their  custom- 
ary environment  into  another  in  which  they  are  struggling  to  adapt 
themselves,  and  to  establish  some  equihbrium  between  themselves 
and  their  host.     The  less  complete  the  adaptation,  the  more  virulent 


112  INFLUENZA 

the  disease  produced.  The  final  outcome  is  a  harmless  parasitism  or 
some  well-established  disease  of  little  or  no  fataHty,  unless  other 
parasites  complicate  the  invasion.  The  logical  inference  to  be  drawn 
from  the  theory  of  a  slowly  progressive  parasitism  would  be  that  in 
the  long  run  mortahty  from  infectious  diseases  would  be  greatly 
reduced  through  the  operation  of  natural  causes.  But  morbidity 
would  not  be  diminished,  possibly  greatly  increased  by  the  wider  and 
wider  diffusion  of  these  parasites,  or  potential  disease  producers.  The 
few  still  highly  mortal  plagues  would  eventually  settle  down  to  sporadic 
infections  or  else  disappear  wholly  because  of  adverse  conditions  to 
which  they  cannot  adapt  themselves. 

"In  this  mutual  adaptation  of  microorganism  to  host,  there  is, 
however,  nothing  to  hinder  a  rise  in  virulence  in  place  of  the  gradual 
decline  if  proper  conditions  exist.  In  fact,  it  is  not  very  difficult  to 
furnish  adequate  explanations  for  the  recrudescence  and  activities  of 
many  diseases  today,  though  the  natural  tendencies  are  toward  a 
decline  in  virulence.  In  the  more  or  less  rapid  changes  in  our  environ- 
ment due  to  industrial  and  social  movements  the  natural  equilibrium 
between  host  and  parasite  established  for  a  given  climate,  locality, 
and  race  or  nationality  is  often  seriously  disturbed  and  epidemics  of 
hitherto  sporadic  diseases  result. 

"These  illustrations  indicate  that  so-called  natural  law  does  not 
stand  in  the  way  of  our  having  highly  virulent  types  of  disease,  if  we 
are  ignorant  enough  to  cultivate  them.  The  microorganism  is  suffi- 
ciently plastic  to  shape  itself  for  an  upward  as  well  as  a  downward 
movement.  Among  the  most  formidable  of  the  obstacles  toward  a 
steady  decline  of  mortahty  is  the  continual  movement  of  individuals 
and  masses  from  one  part  of  the  world  to  another,  whereby  the  partly 
adapted  parasites  become  planted  as  it  were  into  new  soil  and  the 
original  equilibrium  destroyed.  These  various  races  of  disease  germs 
become  widely  disseminated  by  so-called  germ  carriers,  and  epidemics 
here  and  there  hght  up  their  unseen  paths." 

An  example  of  increasing  virulence  from  changing  environmental 
conditions,  is  the  experience  in  the  United  States  Army  camps  in  1917 
and  1918  with  the  streptococcus.  This  microorganism,  which  at  first 
was  but  a  secondary  invader,  particularly  to  measles,  became  so 
exalted  in  virulence  that  it  soon  became  the  cause  of  primary  disease. 
This  is  likewise  true  of  the  various  secondary  invaders  of  the  influenza 
epidemics.  They  become  so  highly  virulent  that  they  dominate  the 
picture  in  the  later  stages.  The  organisms  included  in  this  group  are 
particularly  the  streptococcus,   the  various   pneumococci,   and  the 


AN    EPIDEMIOLOGIC    STUDY  113 

meningococcus.     Probably  the  tubercle  bacillus  should  be  added  to 
this  list. 

It  requires  a  certain  amount  of  time  for  such  organisms  to 
attain  increased  virulence.  The  earliest  cases  in  any  epidemic  are 
comparatively  very  mild.  Thus  Major  Billings,  epidemiologist  at 
Camp  Custer,  says  that  for  the  first  five  days  of  the  autumn  influenza 
epidemic  in  that  camp  the  cases  admitted  to  the  hospital  were  very  mild 
in  character  and  were  recorded  as  simple  bronchitis  and  pharyngitis,  of 
no  great  severity,  the  majority  soon  recovering.  Five  days  after  the 
first  case  was  admitted,  however,  the  entire  symptom  complex  seemed 
to  change,  and  the  cases  admitted  to  the  hospital  from  then  on  were  a 
very  different  and  much  more  severe  type.  Major  Billings,  after 
going  over  the  records,  feels  that  both  types  of  cases  were  the  same 
disease,  the  second  being  a  more  severe  form.  Woolley  reports 
essentially  the  same  condition  from  Camp  Devens. 

The  same  phenomena  were  found  in  1889.  During  the  1889  epi- 
demic Prudden  examined  by  current  bacteriologic  methods  seven 
cases  of  influenza  and  six  cases  of  influenza-pneumonia.  In  them  he 
found  staphylococcus  pyogenes  aureus,  streptococcus  pyogenes, 
diplococcus  pneumoniae,  and  in  other  cases  he  found  a  streptococcus. 
He  concludes  that  the  use  of  culture  methods  and  media  commonly 
employed  has  brought  to  light  no  living  germ  which  there  is  reason  to 
believe  has  anything  to  do  with  causing  the  disease.  He  emphasizes 
the  probable  importance  of  streptococcus  pyogenes  in  particular  in 
inducing  the  various  complications. 

At  this  point  we  should  include  for  the  sake  of  completeness  refer- 
ence to  a  recent  theory  propounded  by  Sahli  explaining  influenza 
epidemics,  a  theory  to  which  we  do  not  subscribe.  He  believes  that 
the  pneumococcus,  the  streptococcus,  the  influenza  bacillus,  and 
possibly  other  organisms,  form  a  complex  group,  an  obligate  complex, 
a  symbiosis,  a  higher  unit,  which  infects  the  organism  as  a  unit.  It  is 
all  of  these  organisms  acting  together  which  produce  the  influenza. 
After  infection  has  occurred  one  or  the  other  member  of  the  group  may 
develop  preferentially.  In  favor  of  this  he  says  that  in  one  of  his 
cases  the  sputum  was  swarming  -uith  influenza  bacilli  on  one  day,  and 
that  the  next  day  the  sputum  was  a  thick  pure  culture  of  the  pneumo- 
coccus. He  says  that  if  an  ultramicroscopic  germ  should  yet  be  dis- 
covered this  would  not  invalidate  the  theory,  but  would  merely  add 
another  member  to  the  group  forming  the  obhgate  complex  virus  unit. 

Meteorologic  conditions. — Formerly  attempts  were  made  to 
demonstrate  etiologic  relationships  between  the  occurrence  of  influ- 


114  INFLUENZA 

enza  and  unusual  conditions  of  the  atmosphere.  In  most  cases  no 
relationship  has  been  discovered.  Nevertheless  it  is  conceivable  that 
the  changes  in  the  atmosphere,  particularly  seasonal  variations,  might 
influence  the  virulence  of  the  organism.  It  has  been  found  that  nearly 
all  of  the  many  epidemics  apparently  originating  in  Russia  took  their 
origin  there  either  in  the  late  autumn  or  in  the  winter  months.  The 
spread  of  influenza  appears  to  be  uninfluenced  by  atmospheric  condi- 
tions, but  the  severity  of  the  disease  is  definitely  increased  in  the  winter 
months,  and  Leichtenstern  believes  that  the  development  of  a  primary 
spread  from  its  point  of  origin  is  also  influenced  by  the  season.  Hirsch 
found  that  out  of  175  correlated  pandemics  or  epidemics,  50  occurred 
in  the  winter  between  December  and  February,  85  in  the  spring  from 
March  to  May,  16  in  the  summer  from  June  to  August  and  24  in  the 
autumn. 

The  soil  plays  no  part  in  the  spread  of  the  disease.  It  prevails 
on  every  soil  or  geologic  formation;  on  the  mountain  top,  in  the  low 
malarial  swamps,  in  the  tropics  and  within  the  arctic  circle.  Volcanic 
eruptions,  fogs,  electrical  conditions,  ozone,  direction  of  the  wind, 
have  all  been  considered  in  previous  epidemics  and  successively 
eliminated  as  etiologic  factors. 

It  must  be  stated,  however,  that  Teissier,  who  investigated  the 
influenza  in  Russia  in  1890  and  has  compared  his  conclusions  at  that 
time  with  the  results  of  investigation  of  the  recent  visitation,  believes 
that  some  particular  cosmic  conditions  suddenly  enhanced  the  viru- 
lence of  an  endemic  etiologic  microorganism — probably  some  ordinary 
germ — and  that  this  opened  the  portals  to  secondary  infections. 

Secondary  invaders. — We  have  considered  a  possible  manner  in 
which  the  virulence  of  the  organism  causing  influenza  may  become 
enhanced.  Whatever  this  organism  may  be,  another  and  equally 
important  virulence  enhancement  occurs  in  the  opportunist  group  of 
the  germs,  so-called  secondary  invaders  of  influenza.  As  we  have 
previously  remarked,  it  is  a  characteristic  of  influenza  outbreaks  in  all 
communities  that  the  earliest  cases  are  very  mild.  Secondary  infection 
has  not  as  yet  obtained  a  foothold.  After  about  a  week  the  charac- 
ter of  the  illness  changes,  becoming  distinctly  more  severe.  Billings 
reported  that  at  Camp  Custer  in  the  autumn  of  1918  cases  admitted 
to  the  hospital  during  the  first  five  days  were  very  mild  in  character  and 
were  reported  as  simply  bronchitis  or  pharyngitis  of  no  great  severity, 
the  majority  soon  recovering.  After  this  time  the  entire  symptom- 
complex  seemed  to  change  and  the  cases  admitted  to  the  hospital 
were  of  a  very  different  and  more  severe  type. 


AN    EPIDEMIOLOGIC    STUDY  115 

Benjafield  reports  that  in  the  Egyptian  Expeditionary  Force  the 
epidemic  commenced  in  May,  1918,  and  that  the  cases  occurring 
during  the  earlier  portion  of  the  epidemic  were  mild  in  type  and  of 
short  duration,  only  a  very  small  proportion  being  complicated  by 
bronchopneumonia.  Wooley  found  at  Camp  Devens  that  the  first 
cases  were  of  a  mild  form  and  were  usually  diagnosed  "naso-pharyn- 
gitis,  acute  catarrhal."  After  a  few  days  the  disease  became  more 
severe  and  pneumonia  cases  developed. 

Bezan9on  found  that  among  the  repatriated  French  soldiers  from 
Switzerland  those  cases  occurring  in  May  and  June  had  a  much  lower 
severity  than  in  the  later  epidemic.  Zinsser's  description  of  the  mild, 
earlier  epidemic  in  Chaumont  has  already  been  quoted. 

The  secondary  invaders  of  pathogenic  importance  are  the  various 
forms  of  the  streptococcus  and  pneumococcus,  the  meningococcus,  the 
staphylococcus,  and  probably  the  tubercle  bacillus  and  the  influenza 
bacillus.  In  the  last  epidemic  as  in  that  of  thirty  years  previously, 
the  chief  compHcations  were  bronchitis  and  pneumonia.  Capps  and 
Moody  found  these  to  be  the  chief  compHcations  in  December,  1915. 
Also  they  found  a  high  incidence  of  sinusitis.  This  has  been  a  feature 
of  the  last  epidemic.  Wooley  cites  a  good  example  of  the  damage  done 
by  these  opportunist  organisms  when  they  are  present.  Among  the 
troops  stationed  at  Camp  Devens  in  the  fall  of  1918  pneumonia  follow- 
ing influenza  was  particularly  prevalent  in  a  battalion  of  negroes  from 
the  South.  This  battalion  had,  a  short  time  previously,  passed 
through  an  epidemic  of  pneumonia  and  Wooley  beheves  that  many  of 
the  blacks  were  harboring  the  pneumococci  which  were  only  awaiting 
a  favorable  opportunity  to  invade  their  hosts.  The  influenza  furnished 
the  required  opportunity. 

That  the  meningococcus  should  be  classed  in  this  group  is  certain. 
The  author  observed  at  Camp  Sevier  cases  of  epidemic  meningitis 
occurring  in  various  influenza  wards  scattered  throughout  the  hospital, 
with  no  demonstrable  relationship.  Usually  there  was  but  one  case  in 
a  ward  and  almost  invariably  meningitis  occurred  when  convalescence 
was  beginning.  No  epidemic  occurred  in  any  ward.  Others  have 
reported  actual  epidemics  of  meningitis  following  influenza.  Moss 
found  that  a  large  proportion  of  his  influenza  cases  had  the  meningo- 
coccus in  the  circulating  blood,  as  demonstrated  by  culture.  Fletcher 
cultivated  meningococci  from  the  lungs  in  all  of  eleven  autopsies,  and 
in  all  eleven  cases  the  influenza  bacillus  was  also  present. 

In  considering  the  effect  of  influenza  on  the  death  rate  in  general, 
and  in  considering  the  relationship  of  influenza  to  other  diseases  in 


116  INFLUENZA 

general,  it  is  important  to  distinguish  those  diseases  which  are  appa- 
rently unrelated  and  those  diseases  which  occur  as  direct  complications 
or  sequelae.  Bronchopneumonia,  bronchitis,  empyema,  otitis  media, 
frequently  tonsillitis  and  sometimes  erysipelas,  occur  as  sequelae. 
Meningitis  should  frequently  be  included  in  this  group. 

Not  only  is  there  an  increase  in  certain  other  diseases  following 
influenza  outbreaks,  genetically  related,  as  we  have  seen,  but  also 
some  observers,  particularly  Crookshank,  beheve  that  previous  to 
epidemic  influenza  prevalences  there  occurs  an  increase  in  the  incidence 
of  other  entirely  unrelated  infectious  diseases,  such  as  poliomyelitis. 
This  theory  of  simultaneous  increase  in  invasiveness  of  many  appar- 
ently unrelated  germs  is  comparatively  new  and  will  probably  receive 
deep  consideration  in  the  future.  For  the  present  the  information  on 
the  subject  is  so  limited  that  attempted  conclusions  would  have  no 
value. 

Origin  of  the  1918  Pandemic. 

In  discussing  the  spread  of  the  1918  pandemic  over  the  earth,  the 
author  has  traced  it  from  an  apparent  origin  in  the  United  States. 
Localized  early  epidemics  are  reported  simultaneously  in  the  United 
States,  France,  and  China.  From  the  literature  at  his  disposal  he  has 
been  unable  to  find  convincing  proof  of  an  earlier  origin  in  Asia,  but 
he  did  emphasize  at  the  time  the  necessity  of  a  much  more  thorough 
study  of  influenza  in  all  countries  to  be  made  by  more  competent 
statisticians.  Nevertheless  it  is  highly  interesting  to  formulate  an 
hypothesis  which  appears  to  meet  all  demands,  on  the  assumption 
that  the  disease  originated  in  America.  In  order  to  hold  a  theory 
with  this  basis  we  must  assume  that  the  third  of  our  previously  men- 
tioned hypotheses  of  the  origin  of  the  disease  is  the  more  nearly  correct. 

Let  us  assume  that  in  the  interpandemic  periods  the  influenza  virus 
is  widely  distributed  over  the  earth,  existing  in  an  avirulent  form. 
The  basis  for  this  assumption  is  the  previously  described  occurrence 
of  localized  epidemics  in  interpandemic  periods.  The  occurrence  of 
solitary  cases,  although  of  interest,  could  scarcely  be  considered  as 
evidence  of  the  widespread  distribution  of  the  virus,  but  in  the  case  of 
the  small  outbreaks  as  in  1900,  1907  and  1915,  and  as  in  the  numerous 
small  outbreaks  described  by  Hirsch,  the  character  of  the  epidemic 
curve  is  characteristic.  Let  us,  then,  assume  that  the  disease  has 
been  endemic  in  the  United  States,  together  with  other  localities. 
It  requires  no  keen  observation  to  discover  in  the  years  1917  and  1918, 
Theobald  Smith's   ''movement  of  individuals  and  masses  from  one 


AN    EPIDEMIOLOGIC    STUDY  117 

part  of  the  world  to  another,  whereby  the  partly  adapted  parasites 
become  planted,  as  it  were,  into  new  soil,  and  the  original  equiHl)rium 
is  disturbed."  Not  only  was  there  a  tremendous  redistribution  and 
concentration  of  individuals  in  our  camps  in  this  country,  but  also 
there  was  a  further  disturbance  of  the  equilibrium  in  the  outbreak 
of  other  infectious  diseases,  particularly  measles.  The  effect  of  the 
measles  epidemic  on  the  virulence  of  the  streptococcus  and  allied 
organisms  has  been  discussed;  presumably  the  same  occurred  with 
respect  to  the  influenza  virus.  Howard  and  Love  report  that  approxi- 
mately 40,512  cases  of  influenza  were  reported  in  the  United  States 
Army  during  1917.     They  write: 

"In  1917,  the  death  rate  for  the  acute  respiratory  diseases  (influ- 
enza, pneumonias  and  the  common  types)  increased  to  1.71.  During 
the  fall  of  1917,  after  the  camps  were  filled  with  drafted  men,  acute 
epidemic  diseases  swept  through  a  number  of  them.  Measles  was  one 
of  the  most  prevalent  and  one  of  the  most  fatal  of  the  infectious  diseases 
that  occurred.  It  was  noted  during  the  fall  and  early  winter  that 
there  were  a  number  of  cases  of  pneumonia  w^hich  were  unlike  the 
pneumonia  that  ordinarily  occurred.  This  was  apparent  both  to  the 
physicians  in  civil  life  and  in  the  army  camps.  It  was  reported  by  all 
classes  of  practitioners  that  numerous  cases  of  pneumonia  were  occur- 
ring which  resembled  the  pneumonia  following  measles,  but  occurring 
among  men  who  had  not  had  measles  recently.  In  a  number  of  the 
camps,  both  in  the  north  and  in  the  south,  rather  extensive  epidemics 
of  pneumonia  occurred  and  a  number  of  deaths  resulted.  The  same 
varietj^  of  pneumonia  occurred  in  the  late  winter  and  spring  of  1918. 
In  many  of  the  camps  pneumonia  was  practically  epidemic  during 
March  and  April.  In  many  camps  a  number  of  cases  occurred  later 
in  the  spring  and  summer.  It  was  again  reported  by  a  number  of 
medical  men  that  these  cases  of  pneumonia  that  were  occurring  were 
different  from  the  types  of  pneumonia  ordinarily  encountered  and  very 
similar  to  pneumonia  following  measles,  but,  again,  that  the  cases 
occurred  among  men  who  had  not  had  measles  recently." 

MacNeal  has  observed  similar  conditions  in  the  American  Expedi- 
tionary Forces  in  France  in  1917: 

"The  American  troops  in  France  in  1917  began  to  show,  as  early  as 
October,  1917,  a  very  considerable  rise  in  the  influenza  morbidity. 
The  data  available  in  the  office  of  the  Chief  Surgeon,  A.  E.  F.,  show 
an  influenza  morbidity  per  100,000  of  321  in  July,  438  in  August,  and 
404  in  September,  rising  to  1,050  in  October,  1,980  in  November, 
and  2,480  in  December,  1917,  in  which  month  the  total  number  of  new 


118  INFLUENZA 

cases  of  influenza  reported  was  3,520.  That  a  considerable  propor- 
tion of  these  cases  were  actual  infections  with  the  bacillus  of  Pfeiffer 
is  proven  by  the  necropsy  findings  in  fatal  cases  of  bronchitis  and 
bronchopneumonia,  especially  those  performed  by  Major  H.  E. 
Robertson  at  Army  Laboratory  No.  1,  Neuf  chateau,  in  November  and 
December,  1917,  and  January,  1918.  In  these  cases  the  bacillus  of 
Pfeiffer  was  found  in  the  scattered  patches  of  lung  involved  in  the 
bronchopneumonia  and  also  with  great  frequency  in  the  cranial  sinuses. 
These  necropsy  findings  were,  at  the  time,  recognized  as  essentially 
new  for  young  adult  Americans,  and,  in  a  discussion  at  Army  Labora- 
tory No.  1,  during  December,  1917,  they  were  considered  as  being  of 
possible  important  significance  for  the  future  morbidity  of  American 
soldiers  in  France.  In  the  British  Army  in  France  there  is  definite 
evidence  of  epidemics  showing  the  same  pathologic  condition,  during 
the  winter  of  1916-17,  and  at  Aldershot  in  September,  1917.  There 
can  be  little,  if  any  doubt  that  this  disease  was  essentially  the  same 
which  attacked  the  American  soldiers  late  in  1917." 

Schittenhelm  and  Schlecht  have  reported  that  a  disease  was 
studied  among  the  German  troops  on  the  Eastern  front  which  resembled 
greatly  the  influenza.  It  occurred  from  the  beginning  of  August  to  the 
middle  of  October,  1917.  It  attacked  simultaneously  and  in  epidemic 
form  units  and  divisions  very  widely  separated  over  a  large  territory. 
It  was  characterized  clinically  by  a  very  sudden  onset,  in  the  greater 
number  of  cases  with  chill,  headache,  pain  in  the  extremities,  some- 
times thoracic  pain  and  cough.  The  fever  lasted  seven  to  nine  days. 
The  spleen  was  enlarged  in  11  per  cent,  of  the  individuals.  There 
was  diarrhea  in  12  per  cent.,  frequently  conjunctivitis,  and  quite 
often  a  scarlatiniform  rash.  Bacteriologic  examination  of  the  blood 
was  negative.  There  was  usually  leucopenia.  No  treatment  seemed 
especially  efficacious.  Aspirin  gave  the  best  results.  The  authors 
call  attention  to  the  close  similarity  to  influenza  and  also  suggest  that 
it  might  have  been  due  to  transmission  by  insects  as  in  pappataci 
fever  or  in  dengue. 

Carnwath  concluded  that  the  finding  of  influenza  bacilli  in  necrop- 
sies in  British  soldiers  in  1917  was  without  epidemiologic  significance  in 
considering  the  origin  of  the  1918  pandemic.  He  had  studied  the 
disease  among  the  British  in  detail  and  appeared  to  be  of  the  opinion 
that  the  first  influenza  morbidity  of  significance  among  the  British 
troops  did  not  appear  previous  to  April,  1918. 

MacNeal  further  says:  "The  influenza  rates  per  100,000  of  1,050 
in  November  and  2,480  in  December,  1917,  really  indicate  a  greater 


AN    EPIDEMIOLOGIC    STUDY  119 

relative  prevalence  of  influenza  at  that  time  in  the  A.  E.  F.  than 
occurred  in  the  fall  of  1918,  when  the  respective  morbidity  rates  were 
826  in  September,  2,176  in  October,  and  1,356  in  November.  The 
total  number  of  American  troops  in  France  was  relatively  small  during 
that  winter — 141,995  effective  mean  strength  in  December — so  that 
the  prevalence  of  influenza  did  not  lead  to  the  recognition  of  an  actual 
epidemic.  Furthermore,  the  over-crowding  in  quarters,  which  seems 
to  have  had  a  definite  relation  to  many  of  the  later  explosive  outbreaks, 
had  not  become  such  a  distinct  feature  at  that  time.  In  addition,  the 
cold,  wet  weather,  exposure  and  unusual  living  conditions  furnished 
explanations  for  the  morbidity  which  were  no  longer  adequate  during 
the  hot  weather  of  May  and  June,  1918.  Until  May,  1918,  therefore, 
the  prevalence  was  that  of  an  endemic  disease,  with  perhaps  an  occa- 
sional outbreak  suggesting  epidemic  character." 

We  admit  that  MacNeal's  report  furnishes  excellent  evidence  of  an 
independent  origin  in  France.  Two  points  should  be  borne  in  mind. 
First,  that  MacNeal's  figures  are  not  for  the  French,  but  for  the 
Americans  who  were  transported  to  that  country,  and  that  we  may 
consequently  consider  influenza  among  the  American  Expeditionary 
Forces  as  being  possibly  from  the  same  source  as  influenza  among  the 
troops  in  our  own  country, — that  the  American  Expeditionary  Forces 
may  be  considered  a  subdivision  of  the  American  Army  in  the  United 
States,  equally  well  as  a  subdivision  of  the  French  population;  second, 
that  we  have  been  unable  to  find  detailed  evidence  of  similar  conditions 
occurring  among  the  French  troops  or  French  population,  where  the 
conditions  have  been  ripe  in  a  way  since  1914.  ]MacNeal  records 
that  in  March  and  April,  1918,  there  was  a  great  increase  in  the  number 
of  troops  brought  over  from  the  United  States  to  France.  Previous 
to  that  time  there  had  been  287,000  in  that  country  and  during  the  two 
months  150,000  w^ere  added,  with  a  consequent  increase  of  more  than 
fifty  per  cent. 

We  should  insert  a  word  of  caution  regarding  the  diagnosis  of 
influenza  among  troops  in  the  absence  of  any  sign  of  an  epidemic. 
Internists  who  served  in  base  hospitals  during  the  war  will  agree  that  a 
diagnosis  of  influenza  is  very  frequently  made  on  the  admission  card 
when  the  disease  turns  out  to  be  some  other  malady.  This  was  not 
equally  true  in  all  camps,  but  regimental  surgeons  could  often  be 
found  who  w'ould  transfer  a  patient  to  the  hospital  with  the  diagnosis 
of  influenza  used  almost  interchangeably  with  the  diagnosis  "Fever 
of  unknown  origin."  It  would  be  interesting  to  see  statistics  from  one 
or  two  of  those  base  hospitals  which  were  manned  with  especially 


120  INFLUENZA 

competent  internists,  as  to  the  frequency  with  which  the  admission 
diagnosis  of  influenza  remained  unchallenged  in  the  hospital,  during  the 
year  1917. 

There  would  be  such  cases  in  greater  or  smaller  numbers.  The 
magnitude  of  this  number  would  not  influence  our  hypothesis. 

Aside  from  this  discussion  of  the  disease  among  our  troops  in  France 
it  is  most  important  that  we  establish,  if  possible,  the  identity  of  the 
disease  reported  among  British  troops  in  Northern  France  during  the 
winter  of  1916-1917  and  designated  by  the  name  "Purulent  Bron- 
chitis." The  disease  first  appeared  in  December,  1916.  It  reached  its 
height  during  February  and  early  March  of  1917,  and  appears  to  have 
disappeared  early  in  the  spring.  Hammond,  Rolland  and  Shore 
report  that  during  February  and  early  March  45  per  cent,  of  the  necrop- 
sies under  observation  showed  the  presence  of  purulent  bronchitis, 
and  they  remarked  that  the  disease  assumed  such  proportions  as  to 
constitute  almost  a  small  epidemic.  They  described  the  clinical 
aspects  as  follows: 

"The  cases  which  came  under  our  notice  can  be  divided  broadly 
into  two  types:  The  first  and  more  acute  presents  a  clinical  picture 
which  closely  simulates  ordinary  lobar  pneumonia  with  a  sustained 
temperature  of  about  103°,  and  expectoration  at  first  blood-streaked — 
rather  than  rusty —  which,  however,  rapidly  becomes  quite  purulent. 
The  pulse-rate  in  these  cases  is  out  of  all  proportion  to  the  temperature 
in  its  rapidity.  Dyspnoea  and  cyanosis  are  prominent  features.  The 
patient  usually  dies  from  'lung  block,'  resulting  in  embarrassment  of 
the  right  side  of  the  heart  on  the  fifth  or  sixth  day.  For  the  last  day 
or  two  there  is  often  incontinence  of  the  feces,  due,  no  doubt,  to  the 
condition  of  partial  asphyxia.  The  mental  state  is  one  of  torpor; 
delirium  is  the  exception. 

"The  second  and  less  acute  type  is  marked  by  a  more  swinging  tem- 
perature with  a  range  of  two  or  three  degrees.  The  expectoration  at 
first  may  be  frothy  and  mucopurulent,  but  it  very  soon  assumes  the 
typically  purulent  character.  This  form  may  run  a  long  course  of 
from  three  to  six  weeks,  during  which  time  the  patient  wastes  a  great 
deal  and  has  frequent  and  profuse  sweats;  indeed,  at  a  certain  stage 
the  illness  is  most  suggestive  of  acute  tubercular  infection,  and  it  is 
only  by  repeated  examination  of  the  expectoration  that  the  clinician 
can  satisfy  himself  he  is  not  really  over-looking  a  case  of  acute  pul- 
monary tuberculosis.  The  majority  of  our  cases  conforming  to  this 
type  have  ultimately  recovered,  but  the  convalescence  is  slow  and 
tedious. 


AN     KIMDEMIOLOCIC    STUDY  IJI 

"Onset. — Whilst  ;i  liistoi-y  ol"  a,  previous  ciitaiiluil  (•.(;n(iitiou  lusting 
lor  ;i  few  days  is  often  obtained,  the  disease  quickly  assumes  an  acute 
cliaracter;  we  have  l)een  able  to  ol)serve  this  in  patients  admitted  into 
this  hospital  with  purulent  bronchitis;  we  find  the  temperature  is 
between  102°  and  103°,  the  pulse  120  or  over,  and  the  respiration  about 
35.  The  patient  frequently  complains  of  shivering  and  looks  pathe- 
tically miserable,  but  we  have  not  seen  an  actual  rigor.  Despite  his 
obvious  shortness  of  breath,  the  sisters  have  noticed  that,  at  any  rate 
at  first,  he  prefers  a  lateral  position  low  down  in  the  bed,  and  resents 
any  attempt  to  prop  him  up. 

"Cough. — This  for  the  first  day  or  two  may  be  irritable  and  dis- 
tressing, with  a  little  frothy  expectoration,  but  as  the  latter  becomes 
more  purulent  the  cough  is  less  troublesome,  and  soon  the" patient  is 
expectorating  easily  and  frequently,  until  the  later  stages  are  reached; 
when  owing  to  increasing  asphyxia  the  patient  liecomes  more  and  more 
torpid,  the  cough  subsides,  and  hardly  any  secretion  is  brought  up. 
This  failure  becomes  an  added  factor  in  bringing  about  a  rapidly  fatal 
termination. 

"Expectoration. — The  sputum,  with  its  yellowish-green  purulent 
masses,  is  very  characteristic,  and  may  be  one  of  the  first  indications 
of  the  serious  nature  of  the  illness  the  patient  is  suffering  from. 

"Temperature. — The  fever  of  this  complaint  does  not  follow  any 
very  constant  type.  In  nearly  all  our  cases  the  pyrexia  was  of  sudden 
onset,  and  for  the  first  few  days  was  more  or  less  sustained  at  about 
103°.  Later  it  conformed  more  to  the  swinging  type  with  a  range  of 
several  degrees.  In  a  few  cases  a  curious  gradual  ante  mortem  drop 
has  been  observed. 

"Pulse. — Tachycardia  is  a  very  constant  feature  throughout  the 
illness.  The  rate  is  frequently  well  over  120,  though  the  volume  may- 
remain  surprisingly  good  until  immediately  before  death. 

"Some  degree  of  dyspnoea  is  always  present,  and  is  usually  pro- 
gressive, though  towards  the  end  in  the  fatal  cases  when  the  mental 
acuteness  is  dulled  by  the  increasing  asphyxia  the  patient  is  not  dis- 
tressed by  its  presence.  In  some  cases  there  have  been  paroxysmal 
exacerbations  of  the  breathlessness,  accompanied  by  a  state  of  panic, 
in  which  the  patient  struggles  wildly  and  tries  to  get  out  of  bed  in 
order  to  gain  relief.  Cyanosis  is  another  prominent  feature  throughout 
the  illness.  At  first  it  may  not  be  more  than  duskiness,  but  in  the 
later  stages  it  becomes  very  evident.  It  is  only  slightly  relieved  by 
oxygen;  this,  no  doubt,  is  partly  explained  by  the  difficulty  in  giving 
the  ox3'gen  efficiently,  owing  to  the  patient's  objection  to  any  mouth- 

10 


122  INFLUENZA 

piece  that  fits  at  all  tightly,  and  partly  by  the  blocked  condition  of 
the  bronchioles  interfering  with  the  absorption  of  the  oxygen. 

'The  condition  usually  begins  with  the  presence  of  a  moderate 
number  of  sharp  crepitant  rales,  often  first  heard  in  the  region  of  the 
root  of  the  lung;  these  quickly  become  generalized.  In  the  majority 
of  the  cases  signs  of  bronchopneumonia  patches  can  be  made  out; 
these  are  generally  situated  near  the  root  of  the  lungs.  In  a  certain 
number  of  cases  these  patches  spread  and  become  confluent,  giving 
practically  all  of  the  physical  signs  of  a  lobar  pneumonia.  As  the 
disease  progresses  the  air  entry  is  diminished;  on  listening  one  is  often 
struck  by  the  small  volume  of  sound  heard.  The  resonance  of  the 
lungs  may  also  be  lessened.  A  slight  pleuritic  rub  was  heard  in  a  few 
of  our  cases,  but  this  was  soon  masked  by  the  bronchitis  signs." 

Detailed  sputum  examination  in  twenty  cases  showed  the  presence 
of  the  influenza  bacillus  in  eighteen,  and  in  ten  out  of  these  eighteen 
the  organism  was  isolated  by  culture.  The  next  most  frequent  or- 
ganism found  was  the  pneumococcus,  which  was  present  in  thirteen 
cases.     The  streptococcus  was  found  in  five. 

Abrahams,  Hallows,  Eyre  and  French  report  the  same  epidemic: 

"A  typical  case  is  as  follows.  The  onset  is  usually  acute;  the 
early  symptoms  are  those  of  a  'cold  in  the  head. '  The  temperature 
may  be  101  or  102°,  but  there  are  no  features  to  distinguish  the  condi- 
tion from  acute  'coryza'  or  febricula,  so  that  in  the  majority  of  cases 
the  patient  does  not  report  sick  for  two  or  three  days,  by  which  time 
he  is  sent  to  the  hospital.  At  this  state  two  features  attract  particular 
attention.  First,  the  character  of  the  expectoration:  this  consists  of 
thick  pale  yellow,  almost  pure  pus,  not  the  frothy  expectoration  famil- 
iar in  ordinary  bronchitis;  it  has  no  particular  odor  and  it  becomes 
increasingly  abundant  until  in  a  day  or  two  it  may  amount  to  several 
ounces  in  the  twenty-four  hours.  Secondly,  the  rapidity  of  the 
patient's  breathing:  this  may  be  so  evident  that  pneumonia  suggests 
itself,  yet  on  examining  the  chest  the  only  physical  signs  consist  of  few 
or  many  rhonchi  scattered  widely,  but  most  marked  at  the  bases  of 
the  lungs  behind,  associated  with  a  wheezy  vesicular  murmur;  reso- 
nance everywhere  is  unimpaired  and  bronchial  breathing  is  absent.  A 
little  later  a  third  point  attracts  notice;  a  peculiar  dusky  heliotrope 
type  of  cyanosis  of  the  face,  lips,  and  ears,  so  characteristic  as  to 
hall-mark  the  nature  of  the  patient's  malady  even  on  superficial 
inspection.  By  this  time  dyspnoea  is  very  pronounced;  respiration 
consists  of  short,  shallow  movements,  which  in  bad  cases  amount 
almost  to  gasps,  reminiscent  of  the  effects  of  gas  poisoning.     Recovery 


AN    EPIDEMIOLOGIC    STUDY  12:^ 

at  tliis  stage  may  ocrur,  hut  by  the  time  the  cyanosis  has  become  at  all 
pronounced  the  prognosis  is  extremely  bad,  though  the  number  of 
days  the  patient  may  still  live,  in  spite  of  the  severity  of  his  distress, 
is  often  surprising.  The  character  of  the  sputum  remains  the  same 
throughout,  though  sometimes  it  is  blood-iinged  or  actual  blood  may 
be  expectorated  instead  of,  or  in  addition  to,  the  more  typical  pale 
yellow  pus.  In  the  later  stages  of  the  illness  areas  of  impaired  note  or 
of  actual  dullness  may  be  found,  particularly  over  the  posterior  aspects 
of  the  lungs,  associated  with  bronchial  breathing  and  crepitant  rales. 
These  may  be  due  to  the  progression  of  the  purulent  bronchitis  into 
hypostatic  pneumonia,  or  into  actual  bronchopneumonia  at  the  bases; 
or,  on  the  other  hand,  they  may  be  due  to  massive  collapse  of  the  lungs 
secondary  to  the  bronchitis  and  obstruction  of  the  bronchioles  by  pus. 
In  a  few  cases,  not  necessarily  the  most  serious,  a  frank  lobar  pneu- 
monia has  developed  later,  and  has  been  followed  by  an  empyema 
from  which  15-30  ounces  of  thin  pneumococcal  pus  has  been  aspirated 
— in  one  case  alone  was  resection  of  a  rib  unavoidable.  The  condition, 
however,  is  not  primarily  a  lobar  or  a  bronchopneumonia,  but  a 
bronchitis,  and  although  a  small  amount  of  basal  bronchopneumonia 
has  been  present  in  one  or  two  of  our  post-mortem  examinations,  in 
other  fatal  cases  there  has  been  no  bronchopneumonia  at  all,  not  even 
the  smallest  portions  of  either  lung  being  found  to  sink  in  water. 

"We  have  no  doubt  that  the  condition  is  primarily  an  affection  of 
the  bronchi  and  bronchioles,  and  not  of  the  alveoli,  though  the  alveoli 
may  be  affected  later  if  the  patient  survives  long  enough.  In  a 
typical  post-mortem  examination  it  would  be  difficult,  or  almost  im- 
possible, to  define  the  actual  cause  of  death  unless  one  knew  the  cUnical 
history." 

Abrahams  and  his  collaborators  describe  in  detail  eight  consecutive 
cases.  A  study  of  the  type  of  onset  may  be  of  help  in  determining  the 
character  of  the  disease.  The  first  patient  had  been  subject  to  bron- 
chitis for  years.  He  had  been  ill  with  cough  and  some  pyrexia  for 
five  days  previous  to  his  admission.  There  is  no  further  description 
of  his  admission  symptoms.  Case  two  was  admitted  on  March  17th, 
having  taken  ill  the  previous  day  with  shivering,  cold  and  pain  in  the 
chest.  The  temperature  was  104°,  the  pulse  rate  118,  and  the  respira- 
tions were  44.  The  patient*was  very  restless  and  had  much  dyspnoea 
but  was  not  cyanosed.  The  third  patient  had  taken  ill  three  days 
previous  to  admission  with  symptoms  of  cold  in  the  head  and  a  sore 
throat.  He  complained  of  headache  and  dry  cough  without  expectora- 
tion, shortness  of  breath,  and  a  pain  behind  the  sternum. 


124  INFLUENZA 

Case  four  was  admitted  with  a  history  of  having  been  out  of  sorts 
with  a  cold  and  bronchial  cough  for  ten  days  previously.  On  admission 
his  temperature  was  103°,  pulse-rate  112  and  respiration-rate  36.  He 
had  abundant  blood-stained  purulent  sputum. 

Case  five  is  the  first  case  that  shows  a  type  of  onset  distinctly 
resembling  that  of  influenza.  The  patient  had  been  ill  three  days  with 
headache,  cough  and  generalized  pain  previous  to  his  admission.  The 
temperature  on  admission  to  the  hospital  was  103°,  pulse-rate  112, 
respiration-rate  20.  There  were  no  abnormal  physical  signs  in  the 
chest  on  admission.,  They  did  appear  two  days  later.  Case  six 
related  that  he  had  been  sleeping  under  canvas  for  three  nights  before 
coming  to  the  hospital,  and  that  during  the  first  of  these  nights  he  was 
taken  ill  with  a  cold  which  became  associated  with  a  cough  and  in- 
creasing shortness  of  breath.  On  admission  there  was  shght  cyanosis, 
and  dyspnoea  was  very  pronounced.  Shortly  afterwards  he  became 
orthopnoeic,  with  heHotrope  cyanosis.  On  the  slightest  exertion,  such 
as  turning  over  in  bed,  the  cyanosis  increased  markedly,  and  although 
the  respiration-rate  remained  under  forty  when  he  was  at  rest,  on 
the  least  exertion  it  increased  to  nearly  sixty.  The  sputum  was 
purulent  and  abundant,  pale  yellow,  not  frothy  and  not  blood-stained, 
and  the  day  after  admission  contained  Bacillus  influenzae,  pneumo- 
coccus  and  Micrococcus  catarrhalis. 

Case  seven  had  been  ill  seven  days  before  admission  with  cough  and 
fever.  On  admission  his  temperature  was  105°,  pulse  116,  respiration 
24.  Case  eight  gave  a  history  of  having  had  a  cough  for  eight  days 
previous  to  admission.  This  cough  had  not  incapacitated  him  much 
at  first,  but  he  became  progressively  worse  during  the  four  days  before 
admission,  with  increasing  shortness  of  breath  and  abundant  yellow 
sputum  which  he  found  it  difficult  to  raise.  On  admission  dyspnoea 
with  cyanosis  was  very  evident. 

Even  from  these  detailed  clinical  descriptions  it  is  impossible  to 
say  definitely  whether  the  disease  was  or  was  not  influenza.  There  is 
no  doubt,  however,  but  that  clinically  the  disease  resembled  more  the 
so-called  streptococcus  pneumonias  that  were  observed  in  the  United 
States  camps  in  the  winter  of  1917-18.  The  descriptions  of  the  mode 
of  onset  are  particularly  at  variance  with  the  onset  as  we  know  it 
in  influenza. 

Those  who  believe  that  the  influenza  bacillus  is  the  cause  of  influ- 
enza maintain  that  the  finding  of  this  organism  in  a  large  per  cent,  of 
cases  by  both  groups  of  observers  is  valuable  evidence.  For  reasons 
previously  stated  we  cannot  agree. 


AN   j:rii)i:MH)LO(;i(j  studv  12') 

Doscriptioii  of  the  opidoiiiic  fciiturcs  is  not  dcluilcd  ciiouuli  t<j  In; 
of  ussistiuicc.  The  first  j^roup  of  iiutliors  rciimik  tluil  the  disease 
constituted  "almost  a  small  epidemic."  The  second  K'oup  say  that 
six  out  of  ei^;ht  cases  in  their  series  of  carefully  reported  patients  came 
from  one  command.  The  former  r(?[)ort  on  twenty  ca.ses,  tlic  latter 
on  eight.  The  latter  remark  that  although  they  have  dealt  with  (m\y 
eight  cases  in  detail,  they  had  a  much  larger  mimher  altogether. 
Presumal)ly  there  were  a  decidedly  larger  nuniher  of  patients  in  both 
hospitals,  but  the  actual  number  is  not  stated.  In  short,  we  do  not 
know  whether  the  disease  appeared  to  be  more  oi-  less  epidemic  than 
the  apparently  similar  di.sease  among  our  troops  in  the  winter  of 
1917-18. 

Both  groups  of  observers  have  described  in  some  detail  the  patho- 
logy of  the  cases  which  were  necropsied.  The  author  in  attempting 
to  obtain  further  comparative  information  has  submitted  the  patholo- 
gic descriptions  given  by  the  British  authors  to  Dr.  E.  W.  Goodpasture, 
who  has  very  kindly  pointed  out  the  points  of  similarity  and  difference 
between  the  gross  and  microscopic  findings  in  these  cases  of  purulent 
bronchitis,  and  the  same  findings  in  typical  influenza.  He  says  that 
the  lung  picture,  as  described,  is  not  the  same  as  that  which  was 
typical  of  the  acute  influenza  observed  in  the  autumn  of  1918  and 
again  in  the  winter  of  1920.  The  characteristic  picture  in  the  latter 
is  primaril}'  an  extensive  involvement  of  the  alveolar  structure,  while 
as  Abrahams  and  his  associates  remarked,  the  condition  in  their  case 
is  primarily  "an  affection  of  the  bronchi  and  bronchioles,  and  not  of 
the  alveoli,  though  the  alveoli  may  be  affected  later,  if  the  patient 
survives  long  enough."  Goodpasture  states  that  the  pathology  as 
described  by  the  British  authors  is  very  similar  to  the  lung  picture  in 
interstitial  bronchopneumonia  described  by  MacCallum  for  the  post- 
measles  and  primary  bronchopneumonia  among  our  troops  in  the 
winter  of  1917-18.  The  streptococcus  and  the  influenza  bacillus  were 
dominant  organisms  in  MacCallum's  series.  It  also  resembles  the 
pathologic  picture  described  by  Pfeiffer  in  his  original  article  on  one  of 
the  late  recurrences  of  the  1889-93  epidemics  of  influenza. 

In  summing  up,  we  must  admit  that  it  is  impossible  to  reach  a 
definite  conclusion,  but  that  both  clinically  and  pathologically  the 
disease  described  among  the  British  troops  in  1916  and  1917  was  not 
typical  of  influenza  as  we  have  known  it  more  recently.  The  similar 
conclusion  reached  by  Carnwath,  presumably  chiefly  from  epidemi- 
ologic considerations,  has  already  been  described.  We  do  not  deny 
that  this    "purulent  bronchitis"  may  have  been  influenza.     On  the 


126  INFLUENZA 

contrary,  it  is  a  part  of  our  hypothesis  that  influenza  under  the  proper 
conditions  may  become  epidemic  in  practically  any  land.  But 
we  do  believe  that  the  evidence  has  not  shown  that  the  disease  among 
the  British  troops  in  1916  and  1917  was  an  etiologic  precursor  of  the 
great  pandemic. 

-To  return  to  a  discussion  of  influenza  in  China,  we  quote  from  an 
article  by  Cadbury  in  the  China  Medical  Journal:  "Unfortunately  no 
health  reports  are  available  for  the  greater  part  of  the  Chinese  Republic. 
We  have  consulted,  however,  the  Health  Reports  of  the  Shanghai 
Municipal  Council  from  1898  to  1917,  and  among  the  total  foreign 
deaths  we  find  that  only  the  following  were  attributed  to  influenza: 
1899,  one  death;  1900,  one  death;  1907,  four  deaths;  1910,  one  death. 
After  this  no  deaths  are  recorded  from  this  cause  up  to  and  including 
the  year  1917. 

"In  the  Hongkong  Medical  and  Sanitary  Reports,  which  give  the 
total  deaths  registered  in  the  Colony,  we  have  examined  the  records 
from  1909  to  1917.  During  these  nine  years  only  two  deaths  were 
attributed  to  influenza,  and  both  occurred  in  1909. 

"From  a  personal  letter  from  Dr.  Arthur  Stanley,  Health  Officer  in 
Shanghai,  dated  February  11,  1919,  I  quote  the  following: 

"  'As  to  influenza  we  had  an  attack  beginning  at  the  end  of  May  and 
lasting  through  June  and  again  in  the  latter  part  of  October  and  lasting 
through  November.  The  latter  was  somewhat  more  severe.  The 
noteworthy  features  were  general  absence  of  catarrhal  symptoms, 
congestive  pharynx  frequent,  as  also  was  a  slight  erythematous  blush 
on  the  neck  and  chest,  which  made  one  think  at  first  of  scarlet  fever. 
Fatal  pneumonia  common  among  the  Chinese  and  Japanese,  but 
among  Europeans/very  Uttle  pneumonia.' 

"In  his  report  for  May,  1918,  Dr.  Stanley  says  that  the  disease  was 
reported  to  have  reached  Peking  before  it  came  to  Shanghai,  but  subse- 
quent reports  showed  that  most  of  the  river  ports  were  almost  simul- 
taneously infected,  the  rate  of  spread  conforming  to  the  rate  of  con- 
veyance by  railways  and  boats  of  infected  persons.  The  mortality 
was  very  low. 

"Newspaper  reports  indicate  that  a  third  appearance  of  the  disease 
in  Shanghai  occurred  from  the  middle  of  February,  1919,  which  was 
still  prevalent  in  April.     The  symptoms  were  much  more  severe. 

"For  Hongkong  I  quote  from  a  personal  letter  from  Dr.  Hickling, 
the  Principal  Medical  Oflacer  of  Health,  dated  January  29,  1919: 

"  'The  epidemic  of  influenza  in  the  spring  was  a  very  mild  one,  so 
far  as  we  can  judge.     The  disease  did  not  last  more  than  a  few  days  in 


AN    KI'IDEMIOLOGIC    STUDY  127 

most  cases.  Tlio  roc-out  opidoniic  (Ootohor,  Xovoinhor,  Dcconiber  and 
January)  has  been  much  more  severe,  often  lasting  two  or  three  weeks.' 

"Only  one  death,  which  occurred  on  May  14th,  was  reported  from 
Hongkong  in  the  spring.  In  the  later  epidemic  the  deaths  reported 
were  as  follows:  October,  70;  November,  95;  December,  67.  The 
first  of  these  deaths  occurred  on  October  oth.  The  figures  for  January 
had  not  been  compiled,  but  the  disease  was  diminishing. 

"Dr.  C.  W.  McKenny  of  Hongkong  has  kindly  furnished  me  with 
the  following  facts:  ' '  'During  the  first  five  months  of  1918  there  were 
twenty-two  admissions  for  influenza  to  the  Civil  and  Tung  Wa  hospitals 
(3  in  May).  In  June  there  were  269  cases  with  three  deaths.  In 
July,  August  and  September,  43  cases;  and  during  October-November, 
130  cases  wath  four  deaths.      .    . 

"  'The  June  epidemic  in  Canton  appeared  first  at  the  Pui  Ying 
School,  then  among  the  emploj'ees  of  the  Post  Office,  the  staff  of  the 
Canton  Hospital,  the  Canton  Christian  College,  and  the  Kung  Yee 
Hospital.  The  other  schools  entirely  escaped.  Eleven  days  were 
taken  by  the  disease  to  spread  from  one  part  of  the  city  to  the  various 
other  parts.'  " 

Plague  appeared  in  the  north  of  China  in  1917,  originating  appar- 
ently in  inner  MongoUa.  The  spread  extended  over  quite  an  area, 
and  it  is  reported  that  this  epidemic  of  pneumonic  plague  has  been 
more  extensive  than  any  since  that  of  1910-11.  The  disease  was 
first  reported  prevalent  in  Patsebolong  December  6,  1917.  The 
diagnosis  was  confirmed  bacteriologically,  and  there  can  be  little 
doubt  but  that  the  cases  of  plague  reported  in  various  parts  of  China 
even  up  to  March  18th  were  true  plague,  and  not  unrecognized 
influenza. 

SECTION  III. 

In  the  following  section  of  our  report  we  shall  have  frequent 
occasion  to  refer  to  a  series  of  investigations  conducted  by  the  author 
in  the  City  of  Boston  during  the  1920  influenza  epidemic.  We  will 
explain  in  some  detail  at  this  point  the  nature  of  the  work  done  and  the 
methods  used,  in  order  that  the  subsequent  references  will  be  readily 
intelligible. 

An  In^-estigation  of  Influenza  in  Boston  During  the 
Winter  of  1920. 

Following  every  widespread  epidemic  interest  centers  in  the  ques- 
tion as  to  how  much  havoc  the  disease  has  wrought,  what  proportion 


128  INFLUENZA 

of  the  population  fell  victim,  and  how  many  of  these  died.  With 
regard  to  influenza  the  vital  statistics  of  all  countries  are  decidedly 
insufficient  in  furnishing  this  information. 

In  nearly  all  countries  influenza  is  not  a  reportable  disease. 
Usually,  as  was  the  case  in  the  United  States  in  1918,  the  disease  was 
made  reportable  during  the  epidemic,  but  this  took  effect  usually  at 
least  two  weeks  after  the  epidemic  had  started  in  a  community. 
Further,  there  is  probably  not  a  single  community  in  which  the  reported 
cases  of  influenza  reach  to  anywhere  near  the  total  of  actual  cases. 
The  question  of  diagnosis,  which  is  not  always  easy  even  in  the  presence 
of  a  pandemic,  causes  some  physicians  to  hesitate  to  report  cases. 
Other  physicians  '  'play  safe  "  and  report  nearly  every  thing  as  influenza. 
Finally,  in  the  period  of  an  epidemic,  the  physicians  are  so  pressed 
with  caring  for  the  sick  that  they  very  naturally  neglect  to  report  cases 
as  they  occur. 

It  becomes  necessary,  therefore,  in  collecting  evidence  in  civil 
populations,  of  the  morbidity  and  fatality  from  influenza,  to  obtain 
additional  information  to  that  available  to  the  Health  Officer. 

The  method  which  may  be  relied  upon  to  give  the  most  accurate 
data  consists  in  house-to-house  surveys  made  soon  after  an  epidemic, 
in  which  competent  inspectors  obtain  detailed  information  concerning 
the  illness  or  freedom  from  illness  of  every  individual  in  the  areas 
canvassed.  The  majority  of  individuals  interviewed  will  not  have 
had  the  disease,  and  it  is  therefore  essential  that  in  such  a  census  a 
large  enough  population  be  covered  that  the  resulting  figures  will  be 
truly  representative  of  the  population  at  large. 

Toward  the  end  of  January,  1920,  when  the  recurrent  epidemic  was 
at  its  height  in  Boston,  the  author  undertook  with  the  aid  of  thirteen 
trained  social  service  workers,  and  one  physician,  who  was  a  graduate 
of  the  Harvard  School  of  Public  Health,  to  make  a  sickness  census  of 
10,000  individuals.  Six  districts  were  chosen  in  different  sections  of  the 
city,  representing  six  different  economic  and  social  groups.  Great 
care  was  exercised  in  selecting  the  districts,  so  that  the  population  in 
each  might  be  as  homogeneous  as  possible  regarding  economic  and 
sanitary  status,  as  well  as  race,   and  living  conditions  in  general. 

We  have  sought  to  clarify  and  to  abbreviate  our  description  of  the 
characteristics  of  the  various  districts  by  incorporating  a  map,  to- 
gether with  photographs  of  typical  streets  in  each  district.  One  who 
compares  these  streets  as  they  are  seen  in  the  photographs  would 
scarcely  find  it  necessary  to  enter  the  buildings  in  order  to  discover 
the  living  conditions  of  the  occupants  (Chart  XIII). 


CHART  XIU. 


T 


LmJIj 


ilf^-A  ^^ 


CHARLE3T0WN^        ^BO^JspN 


]Map  of  greater  Boston  showing  the  distribution  of  the  districts  covered  by  the 
author's  house  census. 


AN    EPIDEMIOLOCIC    STUDY 


129 


District  I  inclutli's  an  Italian  population  of  2,000  iiulividuai.s, 
one-half  of  which  live  in  the  most  congested  portion  of  the  city  (see 
photograph)  known  as  the  North  Kiid,  while  the  other  half,  living  in 
East  Boston,  arc  slightly  less  crowded. 

District  II,  in  South  Boston,  consists  of  2,000  individuals  almost 
entirely  of  Irish  race  stock. 


Fig.  1. — District  1.     Italian  tenements.     Very  congested  and  very  poor. 

District  III,  like  District  I,  consists  of  three  groups  living  in  very 
similar  environment  to  the  two  groups  of  the  first  district,  but  com- 
posed chiefly  of  Jewish  race  stock  of  various  nationalities.  The 
photograph  for  this  district  represents  the  area  in  the  "West  Side" 
near  the  Charles  River  Basin.  The  area  in  the  "South  End"  is  of 
similar  type,  while  the  area  in  East  Boston  is  housed  similarly  to  the 
Italian  district  in  East  Boston.  The  dwellings  in  both  of  these  latter 
districts  correspond  to  those  shown  in  the  second  photograph  of 
District  II. 

While  the  first  three  districts  comprise  tenement  areas,  some  poor 
and  the  remainder  very  poor.  Districts  IV  and  V  represent  the  middle 
class,  and  consist  nearly  entirely  of  "Duplex"  and  "Three-Decker" 
buildings.  The  first  of  these  comprises  1,000  individuals  of  mixed 
race  and  nationality,  the  type  broadly  spoken  of  as  American.  The 
second  consists  of  a  Jewish  population  of  1,600. 


130 


INFLUENZA 


Fig.  2. — District  2.     Irish  tenements.     Congested  and  poor. 


Fig.  3. — Another  street  in  the  Irish  tenement  district. 


AN    EPIDEMIOLOGIC    STUDY 


i:u 


Fig.  4. — District  3.     Jewish  tenements.     Very  congested.     Very  poor. 


Fig.  5. — District  4.     Middle  class.     Mixed  American  population. 


132 


INFLUENZA 


Fig.  6. — District  5.     Middle  class.     Jewish  population.     Moderately  well-to-do. 


Fig.  7. — District  6.     Well-to-do  population.     Mixed  American. 


AX    EPIDEMIOLOGIC    STUDY  133 

In  District  VI  are  included  1,400  individuals  belotising  to  the  well- 
to-do  and  moderately  wealthy  families  of  Broukline, 

The  six  districts  may  be  considered  as  representative  of  the  various 
strata  of  societj^,  so  that  we  are  enabled  to  study  the  influenza  and 
its  mode  of  action  under  varying  environment.  We  have  selected 
areas  in  the  city  consisting  of  households  or  homes  rather  than  boarding 
houses  and  rooming  populations.  After  a  few  attempts  in  the  latter 
group  we  became  convinced  that  the  information  obtained  in  rooming 
houses  was  utterly  valueless.  In  the  Jewish  districts  we  were  able, 
through  the  kind  co-operation  of  the  Federated  Jewish  Charities,  to 
use  trained  Jewish  Social  Service  Workers,  each  of  whom  had  previously 
worked  in  the  district  assigned  to  her,  thereby  possessing  the  con- 
fidence of  the  inhabitants.  They  were  also  able  to  speak  the  language. 
,One-half  of  the  Italian  district  was  surveyed  by  an  ItaHan  physician 
and  the  other  half  by  an  American  Social  Service  Worker  who  knew 
the  Italian  language. 

The  information  obtained  was  recorded  on  printed  forms,  which 
were  filled  out  in  accordance  with  detailed  written  instructions.  Form 
"A"  contained  the  necessary  information  concerning  the  family  as  a 
whole,  including  statistical  data  of  each  individual,  description  of  the 
dwelling,  of  the  sanitary  condition,  of  the  economic  status,  etc.  Form 
"B"  was  filled  out  for  each  individual  and  gave  detailed  information 
as  to  the  occupation  and  illnesses  during  the  1918-19  or  the  1920  in- 
fluenza epidemics,  or  during  the  interval.  Form  "B"  was  so  arranged 
that  the  inspector  was  not  called  upon  to  make  the  diagnosis  of  influ- 
enza, but  to  record  the  various  symptoms  as  described  by  the  patient. 
The  decision  as  to  the  diagnosis  was  made  later,  by  the  author.  All 
blank  spaces  were  filled  in  with  either  a  positive  or  negative  answer, 
so  that  the  reviewer  knew^  that  all  questions  had  been  asked  and 
answered.     (See  Appendix.) 

The  inspection  was  begun  on  February  9th,  at  the  height  of  the 
epidemic.  All  records  were  turned  in  and  reviewed  by  the  author, 
who  blue-penciled  obvious  inaccuracies  and  incorporated  directions 
and  questions  in  those  instances  where  he  desired  further  information. 
The  records  w^ere  then  returned  to  the  inspectors  who,  at  the  termina- 
tion of  the  epidemic  early  in  March,  surveyed  the  entire  10,000  a 
second  time,  checking  up  their  first  record,  correcting  any  inaccuracies, 
and  adding  records  of  additional  cases  of  influenza  which  had  occurred 
in  the  interval. 

The  most  careful  statistical  surveys  and  compilations  are  not  with- 
out error.     We  have  gone  into  considerable  detail  in  the  preceding 


134  INFLUENZA 

description  in  order  to  demonstrate  the  several  checks  that  have  been 
made  upon  the  work,  without  which  information  others  would  be 
unable  to  judge  of  the  accuracy  or  value  of  our  work. 

Diagnostic  standards  for  the  1918  epidemic. — All  cases  of  illness 
recorded  on  the  reports,  which  have  occurred  during  either  the  1918  or 
the  1920  epidemics,  or  in  the  intel'val  between  them,  have  been  put 
into  four  groups  as  regards  diagnosis  of  influenza.  Cases  are  desig- 
nated as  "Yes,"  ''Probable,"  "Doubtful,"  and  "No." 

Cases  of  illness  occurring  during  the  months  of  1918  and  1919  in 
which  influenza  was  epidemic  and  in  which  the  patient  remembers 
that  he  had  the  more  definite  symptoms,  (fever,  headache,  backache, 
pain  in  the  extremities,  pneumonia)  and  in  which  he  was  sick  at  least 
three  days  and  in  bed  at  least  one  day,  have  been  designated  as  "Yes. " 
The  symptoms  chosen  are  those  most  likely  to  be  remembered.  The 
individual  frequently  does  not  remember  all.  Statements  of  the 
absence  of  fever  are  often  unreliable.  Usually  the  headache,  backache 
or  pain  in  the  extremities,  or  even  all  of  these  are  well  recollected. 

Cases  occurring  particularly  during  the  epidemic  period  in  which 
the  more  definite  symptoms  are  unknown,  but  who  were  sick  three 
days  or  longer  and  who  were  in  bed  at  least  one  day,  were  probably 
influenza.  This  is  particularly  true  if  there  were  no  other  symptoms 
suggestive  of  some  other  definite  disease.  Such  cases  were  designated 
"Probable." 

Cases  have  been  designated  as  doubtful  when  the  evidence  of 
illness  falls  short  of  the  above  desiderata.  Cases  of  true  influenza 
may  fall  into  this  group,  either  because  of  the  extreme  mildness  of  the 
symptoms  and  course  or  because  of  the  inaccurate  memory  of  the 
individual  concerning  the  events  of  his  illness  sixteen  months  previ- 
ously. Our  results  show  that  the  group  of  doubtful  cases  is  relatively 
very  small  and  the  number  of  true  cases  lost  in  this  group  will  be 
negligible. 

One  important  reason  for  adhering  to  the  above  classification  is 
that  it  corresponds  closely  with  that  used  by  Frost  and  Sydenstricker, 
so  that  our  results  may  easily  be  compared  with  theirs. 

Standards  for  1920. — For  1920  the  illnesses  were  so  recent  in  the 
minds  of  the  patients  that  we  have  required  rather  full  information 
for  making  the  diagnosis  of  "Yes."  For  this  designation  certain 
symptoms  are  arbitrarily  required.  Certain  additional  symptoms, 
if  present,  serve  to  strengthen  the  diagnosis  of  influenza.  The  required 
symptoms  are  fever,  confinement  to  bed  for  one  day  or  more  and  at 
least  two  out  of  the  following  three,  headache,  backache  and  pain 


AN    EPIDEMIOLOGIC    STUDY  135 

in  the  extremities.  The  additional  symptoms  which  influence  the 
classification  are  sudden  onset,  prostration,  lachryrnation,  epistaxis, 
and  cough. 

Cases  designated  as  probable  are  those  in  which  the  symptoms  as 
enumerated  above  are  incomplete  in  one  or  more  details,  but  yet  in 
which  the  diagnosis  of  influenza  would  be  justified.  "Probable," 
therefore,  means  that  the  case  is  to  be  accepted  among  the  hst  of  true 
influenza  cases.  This  is  particularly  so  when  the  case  occurs  during 
the  epidemic  period. 

"Doubtful"  applies  to  those  cases  in  which  the  evidence  although 
suggestive  of  influenza,  is  not  complete  enough  to  warrant  such  a 
diagnosis.  The  doubtful  feature  may  be  in  the  lack  of  too  great  a 
number  of  the  symptoms  enumerated,  or  the  presence  of  symptoms 
which  might  be  due  to  some  other  disease.  Certain  cases  occurring 
at  the  same  time  with  other  cases  of  typical  influenza  in  the  same 
household,  and  which  would  otherwise  have  been  recorded  as 
doubtful,  have  been  marked  either  "Probable"  or  "Yes." 

Standards  of  severity. — A  purely  arbitrary  classification  of  severity 
has  been  adopted.  Probably  no  two  observers  would  agree  exactly 
on  a  classification  of  this  nature,  but  for  the  purposes  of  this  study  the 
following  will  suit  all  requirements  provided  the  standard  used  is 
carried  in  mind  throughout  the  comparison. 

If  a  patient  with  influenza  is  under  medical  care,  and  the  case  is  one 
of  ordinary  severity,  the  usual  period  in  which  the  individual  is  advised 
to  remain  in  bed  is  one  week.  This  is  the  basis  of  the  criteria  of 
severity. 

Mild. — A  case  is  recorded  as  mild  if  the  individual  has  remained 
in  bed  three  days  or  less;  Average,  if  in  bed  four  to  seven  days;  Severe,  if 
in  bed  over  seven  days.  Pneumonia.  This  designation  is  added  to 
that  of  "severe"  only  in  case  the  physician  made  such  a  diagnosis, 
or  if  the  evidence  under  "symptomatology"  leaves  no  doubt  as  to  the 
condition. 

Examples  of  individual  exceptions  to  the  preceding  general  classi- 
fication are  as  follow^s:  An  individual  in  bed  two  days,  but  sick  for 
three  weeks  might  be  recorded  as  average.  A  mother,  with  a  family 
of  sick  children  and  who  spent  no  time  in  bed  may  have  been  "a  severe 
case  of  influenza.  In  fact,  we  have  allowed  ourselves  a  certain  latitude 
in  individual  cases  in  classifying  both  the  diagnosis  and  the  severity 
of  the  disease. 

In  the  final  tabulation  we  have  included  both  the  "Yes"  and  the 
"Probable"  as  being  cases  of  influenza.     This  has  been  done  after  a 
careful  comparison  of  both  groups. 
11 


136  INFLUENZA 

As  a  check  upon  the  reUabiHty  of  the  work  we  have  compared  our 
results  for  the  1918  epidemic  with  those  reported  by  Frost  and  Syden- 
stricker  and  have  discovered  that  with  regard  to  the  general  subject 
discussed  in  both  studies  there  is  close  agreement.  This  is  important 
in  view  of  the  long  period  that  has  elapsed  between  the  first  pandemic 
and  the  time  of  our  survey,  and  because  we  are  unable  to  compare 
our  tables  of  incidence  for  1918  with  those  for  the  city  or  the  state  at 
large.  Our  own  records  do  not  place  the  date  of  occurrence  of  the 
disease  in  1918  any  more  closely  than  by  month. 

We  have  compared  our  1920  incidence  curves  with  those  of  Massa- 
chusetts and  find  a  close  correspondence,  particularly  in  the  date  of 
onset,  peak,  and  disappearance  of  the  epidemic.  We  have  done 
likewise  for  the  occurrence  of  the  disease  in  the  city  of  Boston  at 
large  (Chart  XIV). 

In  the  past  but  few  house-to-house  canvasses  have  been  made 
with  relation  to  influenza.  Auerbach,  following  the  1889  epidemic, 
collected  statistics  on  200  families  distributed  throughout  the  city 
of  Cologne.  Abbott,  while  not  conducting  a  canvass,  did  obtain  a 
certain  amount  of  valuable  information  by  letters  addressed  to 
physicians,  institutions  and  corporations  throughout  the  State  of 
Massachusetts. 

There  is  fairly  abundant  hterature  on  the  disease  as  it  occurred  in 
institutions.  Moody  and  Capps,  in  a  study  of  the  epidemic  in  Chicago 
in  December,  1915  and  January,  1916,  made  a  survey  of  the  personnel 
and  inmates  of  four  institutions  in  that  city.  Among  other  rather 
numerous  statistical  compilations  from  institutions  we  may  mention 
that  of  Hamilton  and  Leonard  which  was  devoted  particularly  to 
a  study  of  immunity,  and  that  of  Stanley  at  San  Quentin  Prison, 
California. 

Garvie  has  reported  his  personal  experience  with  influenza  in  an 
industrial  area  and  discusses  the  disease  as  it  has  occurred  in  families 
in  his  private  practice. 

Carnwath  reports  a  "block  census"  undertaken  by  Dr.  Niven  in 
Manchester,  England.  This  is  of  the  same  nature  as  our  own  work. 
Reeks  has  made  a  detailed  house  survey  of  2,757  persons  in  New 
Britain,  Connecticut.  D.  W.  Baker  has  conducted  somewhat  similar 
surveys  for  the  New  York  Department  of  Health,  and  Winslow  and 
Rogers  quote  the  excellent  record  of  the  Visiting  Nurse  Association 
of  New  Haven,  in  which  they  have  information  for  all  of  the  families 
cared  for  by  the  nurses.  This,  however,  is  a  collected  group  and  does 
not  correspond  with  the  so-called  block  census. 


CHART  XIV 


^853 


^2^ 


Chart  showing  the  actual  incidence  of  influenza  in  Boston  by  weeks  and  the 
actual  incidence  among  the  10,000  individuals  sur\-eyed  by  weeks  during  the  first 
three  months  of  1920. 

Full  Line — incidence  in  the  entire  city  based  upon  reports  to  the  Health^Com- 
missioner. 

Dotted  Line — incidence  in  the  six  districts  surveyed. 


AN    EPIDEMIOLOGIC    STUDY  137 

The  most  comprehensive  and  detailed  work  that  has  been  done  in 
this  line  is  that  reported  by  Frofet  and  Sydenstricker  and  by  Frost, 
the  first  being  the  result  of  a  canvass  of  46,535  persons  in  Maryland, 
and  the  second  a  similar  report  based  on  a  canvass  of  130,033  persons  in 
several  different  cities  of  the  United  States.  We  shall  have  occasion 
to  refer  to  these  later. 

Morbidity. 

There  has  been  great  actual  variation  in  the  morbidity  from  influ- 
enza in  the  various  epidemics  and  even  in  different  localities  during 
single  epidemics.  Previous  to  1889  there  were  no  reliable  statistics 
for  the  disease  incidence,  and  subsequent  to  that  date  the  records, 
for  the  reasons  previously  mentioned,  have  still  been  not  entirely 
adequate. 

In  the  history  of  influenza  morbidity,  as  in  that  of  its  mortality, 
we  must  content  ourselves  for  information  prior  to  the  nineteenth 
century  with  the  very  general  estimates  made  by  contemporary' 
historians.  During  the  last  centurj^  the  statistics  have  been  more 
numerous  and  more  nearly  correct.  As  far  back  as  the  first  recognized 
pandemic,  1510,  the  extremely  high  morbidity  has  been  a  recognized 
characteristic.     Thomas  Short  in  speaking  of  this  pandemic  says, 

"The  disease attacked  at  once  and  raged  all  over  Europe, 

not  missing  a  family  and  scarce  a  person. " 

Pasquier  in  1557  spoke  of  the  disease  as  common  to  all  individuals, 
and  Valleriola  describes  the  widespread  distribution  of  the  epidemic 
throughout  the  whole  of  France  during  that  year.  It  spared  neither 
sex,  age,  nor  rank,  neither  children  nor  aged,  rich  nor  poor.  The 
mortahty,  however,  was  low,  "children  only,  dying. "  Again,  Thomas 
Short  remarks,  "This  disease  seized  most  countries  very  suddenly 
when  it  entered,  catching  thousands  the  same  moment. " 

Of  the  second  pandemic,  1580,  Short  says,  "Though  all  had  it,  few 
died  in  these  countries  except  such  as  were  let  blood  of,  or  had  unsound 
viscera. " 

Thomas  Sydenham  remarks  that  in  the  epidemic  of  1675  no  one 
escaped,  whatever  might  be  his  age  or  temperament,  and  the  disease 
ran  throughout  whole  famiUes  at  once. 

MoUneux  recorded  concerning  1693,  "All  conditions  of  persons 
were  attacked,  those  residing  in  the  country'  as  well  as  those  in  the 
city;  those  who  lived  in  the  fresh  air  and  those  who  kept  to  their  rooms; 
those  who  were  very  strong  and  hardy  were  taken  in  the  same  manner 
as  the  weak  and  spoiled;  men,  women  and  children,  persons  of  all 
ranks  and  stations  in  Life,  the  youngest  as  well  as  the  oldest." 


138  INFLUENZA 

Schrock  tells  us  that  in  Augsburg  in  1712  not  a  house  was  spared 
by  the  disease.  According  to  Waldschmidt  in  Kiel,  ten  and  more 
persons  were  frequently  taken  ill  in  one  house,  and  Slevogt  says  that 
the  disease  was  fearful  because  so  many  persons  contracted  it  at  the 
same  time.  The  disease  was,  however,  not  dangerous,  for  Slevogt 
continues:  "Fear  soon  vanished  when  it  was  seen  that  although  it 
had  spread  all  over  the  city,  it  left  the  sick  with  equal  rapidity." 

It  is  estimated  that  in  the  epidemic  of  1729-1730,  60,000  people 
developed  the  disease  in  Rome,  50,000  in  Mayence,  and  14,000  in 
Turin.  In  London  "barely  one  per  cent,  escaped."  In  Lausanne 
one-half  of  the  population,  then  estimated  at  4,000,  was  stricken.  In 
Vienna  over  60,000  persons  were  affected.  In  the  monasteries  of 
Paris  so  many  of  the  inmates  were  suffering  from  the  disease  that  no 
services  could  be  held. 

Huxham  is  quoted  in  Thomson's  "Annals"  as  declaring  concerning 
the  epidemic  of  1732-33:  "Not  a  house  was  free  from  it,  the  beggar's 
hut  and  the  nobleman's  palace  were  ahke  subject  to  its  attack,  scarce 
a  person  escaping  either  in  town  or  country;  old  and  young,  strong  and 
infirm,  shared  the  same  fate." 

Finkler  writes  as  follows  concerning  the  epidemic  of  1758:  "On 
Oct.  24th,  Whytt  continues,  the  pestilence  began  to  abate.  He  is  not 
sure  whether  this  was  due  to  a  change  in  the  weather,  or  because  the 
disease  had  already  attacked  most  people,  although  the  latter  seems 
more  plausible  to  him,  particularly  as  he  says  that  'in  Edinburgh 
and  its  vicinity  not  one  out  of  six  or  seven  escaped, '  and  in  other  locali- 
ties it  is  said  to  have  been  even  worse.  In  the  north  of  Scotland  also, 
the  epidemic  was  greatly  disseminated  from  the  middle  of  October  to 
the  end  of  November.  A  young  physician  wrote  to  Robert  Whytt: 
'It  was  the  most  universal  epidemic  I  ever  saw,  and  I  am  persuaded 
that  more  people  were  seized  with  it  than  escaped. '  This  same  physi- 
cian reported  that  'it  was  not  at  all  mortal  here.'" 

In  the  epidemic  of  1762,  we  learn  from  Razoux,  de  Brest,  Saillant, 
Ehrmann,  that  the  morbidity  was  great  while  the  mortahty  was  low. 

According  to  Grimm,  nine-tenths  of  the  inhabitants  of  Eisenach 
contracted  the  disease  in  1767. 

Daniel  Rainy,  of  Dubhn,  in  describing  the  invasion  of  an  institu- 
tion in  1775-76,  tells  us  that  from  among  367  persons  varying  in  age 
from  12  to  90  years,  200  were  taken  sick.  Thomas  Glass  says: 
"There  sickened  in  Exeter  Hospital  all  the  inmates,  one  hundred  and 
seventy-three  in  number;  one  hundred  and  sixty-two  had  coughs. 
Two  or  three  days  after  the  hospital  was  invaded  the  city  workhouse 


AN    EPIDEMIOLOGIC    STUDY  139 

was  attacked;  of  the  two  hundrod  paupers  lioused  there  oidy  very  few 
escaped  the  disease." 

Gilibert  described  an  extraordinary  morbidity  in  llu.s.sia  in  1780-81. 

Metzger  says  that  in  1782  the  Russian  catarrh  was  so  universal 
during  the  month  of  March  that  in  many  houses  all  the  inhabitants 
were  attacked.  During  this  period,  "in  St.  Petersburg,  30,000,  and 
in  Konigsberg,  1,000  persons  fell  ill  each  day;"  in  Rome  two-thirds 
of  the  inhabitants  were  attacked;  in  Munich,  three-fourths;  and  in 
Vienna  the  severity  of  the  epidemic  compelled  the  authorities  to  close 
the  theaters  for  eight  days. 

The  epidemics  of  1788-89,  1799-1800  and  of  1802-1803  were 
characterized  by  a  relativelj^  lower  morbidity  than  that  of  1830-32,  in 
which  the  morbidity  was  again  enormous.  Likewise  in  1833,  the 
morbidity  was  very  great.  In  Prague  "scarcely  a  house  was  spared 
by  the  plague."  In  Petrograd,  10,000  persons  were  attacked;  in 
Berlin  at  least  50,000.  These  are  the  figures  of  Hufeland.  The 
Gazette  ]Medicale  records  the  morbidity  as  being  four-fifths  of  the  total 
number  of  inhabitants  of  Paris. 

In  1836,  according  to  Gluge,  40,000  persons  suffered  from  the 
disease  in  Berlin  alone. 

In  London,  in  the  1847  epidemic,  it  has  been  calculated  that  at 
least  250,000  individuals  took  sick,  and  in  Paris,  according  to  Marc 
d'Espine,  between  one-fourth  and  one-haK  of  the  population  developed 
the  disease,  and  in  Geneva  not  less  than  one-third. 

Leichtenstern  informs  us  that  in  1890  the  early  reports  were  made 
by  clinical  men  and  were  mere  presumptions.  They  were  almost 
universally  higher  than  the  later  statistical  findings.  The  early  esti- 
mates for  the  morbidity  in  several  German  cities  were  from  40-50  per 
cent.  On  the  other  hand,  one  of  the  highest  statistical  reports  recorded 
by  Leichtenstern  was  for  Strasbourg  in  which  36.5  per  cent,  of  the 
individuals  became  sick.  The  average  morbidity  reported  by  him  ran 
between  20  and  30  per  cent.  The  difference  is  accounted  for  in  part 
by  the  fact  that  some  of  the  very  mild  cases  were  not  recorded  in  the 
statistics,  and  in  part  by  the  tendency  in  giving  estimates,  to  exaggerate. 

Auerbach  has  collected  the  statistics  of  200  families  distributed 
throughout  the  city  of  Cologne.  He  found  that  149  of  these  families 
(75  per  cent.)  were  attacked.  In  these,  235  were  ill — 59  men,  95 
women,  and  81  children.  The  larger  number  of  women  was  explained 
as  due  to  the  illness  of  the  female  servants.  He  estimates  each  family 
as  consisting  on  an  average  of  six  individuals,  and  concludes  that  20 
per  cent,  were  taken  with  the  disease. 


140  INFLUENZA 

Following  the  1889  epidemic,  Abbott  concluded,  on  a  basis  of  ques- 
tionnaries  sent  out  to  various  individuals  and  institutions  in  the  State 
of  Massachusetts,  that  39  per  cent,  of  the  entire  population  had  been 
attacked,  in  all  about  850,000  persons. 

Moody  and  Capps,  in  December,  1915,  and  January,  1916,  made  a 
survey  of  the  personnel  and  inmates  of  four  institutions  in  Chicago, 
the  Michael  Reese  Hospital,  the  Illinois  Training  School  for  Nurses, 
the  Old  Men's  Home,  and  St.  Luke's  Hospital  Nurses  Training  School, 
making  a  total  of  677  persons  surveyed,  of  whom  144  developed 
influenza,  making  a  percentage  morbidity  of  21.  They  remarked 
that  there  were  many  others  with  colds  who  remained  on  duty  and 
were  not  included  in  the  table  and  were  not  diagnosed  as  influenza. 

We  have  already  described  the  relatively  low  morbidity  and 
mortality  in  the  early  spring  epidemic  in  the  United  States.  Accord- 
ing to  Soper,  the  total  number  affected  in  March,  1918,  at  Camp 
Forrest  and  the  Reserve  Officers  Training  Camp  in  the  Oglethorpe 
Camps  was  estimated  at  2,900.  The  total  strength  at  that  time  was 
28,586.  The  percentage  morbidity  then  was  probably  a  little  over 
10  per  cent.  Dunlop,  in  describing  the  May,  1918,  epidemic  in  Glas- 
gow, says  that  it  was  more  limited  in  extent,  as  well  as  milder,  than  the 
later  epidemic. 

It  has  been  estimated  that  in  the  autumn  epidemic  in  the  United 
States  Army  Camps  one  out  of  every  four  men  had  influenza,  and  one 
out  of  every  twenty-four  men  encamped  in  this  country  had  pneumonia. 
During  the  four  autumn  months  of  1918,  338,343  cases  of  influenza 
were  reported  to  the  Surgeon  General's  Office;  there  were  61,691  cases 
of  pneumonia. 

WooUey  reports  that  among  the  soldiers  at  Camp  Devens,  Mass. 
30  per  cent,  of  the  population  was  affected. 

At  Camp  Humphreys,  16  per  cent,  of  the  entire  personnel  developed 
the  disease.  The  camp  had  an  average  strength  of  26,600  individuals. 
Fifty-two  per  cent,  of  the  entire  number  of  cases  occurred  during  the 
peak  week,  which  ended  October  4th.  The  outbreak  began  September 
13th  and  ended  October  18th. 

Hirsch  and  McKinney  report  that  an  epidemic  of  unusual  virulence 
swept  with  great  rapidity  through  several  organizations  in  Camp 
Grant  between  September  21,  1918,  and  October  18,  1918.  During 
this  time  9,037  patients  were  admitted  to  the  Base  Hospital,  repre- 
senting about  one-fourth  of  the  strength  of  the  camp,  and  of  these, 
26  per  cent,  developed  pneumonia.  About  11  per  cent,  of  the  total 
admissions  or  43  per  cent,  of  the  total  cases  of  pneumonia  died. 


AN    EPIDEMIOLOGIC    STUDY  141 

Referring  to  the  report  of  Howard  and  Love,  we  quote  as  follows: 
"It  is  probable  that  practically  all  susceptible  human  material  in 
infected  camps  suffered  from  an  attack  of  the  disease  during  the  con- 
tinuance of  the  epidemic.  The  records  from  various  camps  indicate 
that  from  15  to  40  per  cent,  of  commands  suffered  from  an  attack  of 
the  disease.  These  records,  as  previously  stated,  do  not  indicate  in 
full  the  true  incidence  of  the  disease.  Certain  good  results  were 
accomplished  in  some  camps  by  the  application  of  effective  and  early 
isolation  of  patients  and  suspects  and  other  measures  generally  recog- 
nized as  of  value.  It  was  sometimes  possible  to  retard  the  progress  of 
the  epidemic  and  cause  it  to  be  spread  over  a  longer  period  of  time. 
The  epidemic  thus  became  less  explosive  in  character,  and  fewer  people 
were  under  treatment  at  the  same  time.  It  was  possible  to  take 
better  care  of  the  sick  and  thus  reduce  the  incidence  of  and  deaths 
from  compUcating  pneumonia.  It  has  not  been  shown  that  such 
measures  accomplished  reduction  in  the  absolute  number  of  cases  of 
influenza  occurring  in   one   command   as   compared   with   another. 

"The  'cantonment'  group  of  camps  gave  a  much  higher  death  rate 
from  influenza  and  its  complications  than  the  'tent'  camp  or  'depart- 
mental' group.  At  first  glance  it  would  appear  that  the  different  hous- 
ing conditions  and  the  more  marked  overcrowding  in  cantonments 
at  the  time  would  fuUy  account  for  this  divergence.  Closer  study, 
however,  leads  to  the  conclusion  that  geographical  location  was  a 
factor  of  equal  or  greater  importance.  It  is  well  known  that  the 
disease  was  most  virulent  and  fatal  in  the  northern,  eastern  and  middle 
west  states,  a  district  in  which  cantonments  predominated.  In  the 
southern  and  Pacific  coast  states,  where  the  most  of  the  tent  camps 
were  located,  a  milder  type  of  the  disease  prevailed,  wdth  fewer  resultant 
fatahties.  Camp  Lewis,  Washington,  and  Camp  Gordon,  Georgia 
(both  cantonments),  had  relatively  low  death  rates,  approximating 
those  in  nearby  tent  camps.  On  the  other  hand,  Camp  Syracuse, 
New  York,  and  Camp  Colt,  Pennsylvania  (both  tent  camps),  suf- 
fered severely  and  reported  death  rates  approximating  those  of  canton- 
ments in  the  same  geographical  district." 

Three  waves  of  influenza  are  reported  by  Stanley  at  San  Quentin 
Prison.  During  the  early  wave  it  was  estimated  that  over  500  of  the 
1,900  men  in  the  prison  population  were  ill.  The  wave  lasted  for  a 
Uttle  over  two  weeks.  In  the  second  epidemic  there  were  69  cases  in 
all,  ten  per  cent,  of  which  developed  pneumonia,  with  two  deaths. 
There  were  fewer  ambulatory  cases  than  in  the  first.  Three  and 
seven-tenths  per  cent,  of  the  population  was  attacked  in  the  second 


142  INFLUENZA 

epidemic,  as  compared  with  27  per  cent,  in  the  first.  In  the  third 
epidemic  there  were  59  cases,  with  no  pneumonia  and  no   deaths. 

Hernando  estimates  that  in  the  Phihppine  Islands,  40  per  cent,  of 
the  total  population  of  7,000,000  was  stricken  with  the  disease.  The 
epidemic  began  in  June,  although  it  did  not  become  severe  until 
October.  The  group  of  ages  that  suffered  most  were  those  between 
ten  and  twenty-nine  years.  Hernando  does  not  believe  that  the 
disease  was  imported  because  cases  were  reported  before  ships  arrived 
from  infected  countries.  After  the  importation  of  cases  from  elsewhere 
the  disease  assumed  the  more  severe  form. 

Armstrong,  in  reporting  a  survey  of  700  influenza  convalescents  in 
Framingham,  Mass.,  remarked  that  16  per  cent,  of  the  entire  popula- 
tion were  infected  with  influenza.  Reeks,  in  a  house  survey  in  New 
Britain,  Connecticut,  found  from  among  2,757  persons  that  the  mor- 
bidity rate  reached  234  per  thousand.  Dr.  Niven  found  in  his  block 
census  in  Manchester,  England,  that  of  4,721  individuals,  1,108 
(25  per  cent.)  had  developed  the  disease.  Fourteen  and  eight-tenths 
per  cent,  of  the  population  were  attacked  in  the  summer  and  10.4  per 
cent,  during  the  autumn  and  winter. 

Frost  found  in  his  survey  of  130,033  individuals  that  the  percent- 
age of  the  population  attacked  varied  from  15  per  cent,  in  Louisville, 
Ky.,  to  53.3  per  cent,  in  San  Antonio,  Texas,  the  aggregate  for  the 
whole  group  being  about  28  per  cent.  He  remarks  that  this  agrees 
with  scattered  observations  in  the  first  phase  of  the  1889-1890  epi- 
demic, when  the  attack  rate  seems  to  have  varied  within  these  limits. 
In  five  of  the  localities  studied,  geographically  widely  separated,  the 
incidence  rate  varied  only  within  a  narrow  limit,  from  200  to  250  per 
thousand.  Variations  in  attack  rate  showed  no  apparent  consistent 
relation  to  geographic  location  or  size  of  community,  or  to  the  rapidity 
of  development  of  the  epidemic. 

In  a  house-to-house  survey  of  10,000  individuals  in  Boston  the 
author  found  that  in  the  winter  of  1918-19,  19.71  per  cent.,  or  one- 
fifth  of  the  entire  population  had  developed  the  disease.  It  should  be 
pointed  out  that  while  the  standards  used  in  this  survey  are  entirely 
comparable  to  those  used  by  Frost,  the  author  has,  contrary  to  Frost's 
method,  not  included  in  his  group  of  positive  cases  those  classified 
as  "doubtful."  This  would  raise  the  total  incidence  to  a  certain 
extent,  but  we  feel  convinced  that  by  omitting  the  doubtful  cases  we 
have  approached  nearer  to  a  correct  picture  of  the  epidemic  as  it 
actually  occurred.  As  will  be  seen  from  Chart  XVI  there  was  no  great 
variation  in  the  different  districts  studied,  with  the  exception  of  Dis- 


CHART  XV. 


land  Z 

Influenza 
incidence 
in  10,000 
individ- 
uals [both 
epidemics 

1 

'/A 
1 

I 

v/. 

1 

Z 

Mdle 
Percent 

18.25 

8-7  6 

2.0  8 

19.71      9.b5"     2.^0 

Femd  le 
Percent 

21.11 

10.29 

2  70 

1 

Male    VFemale 

1918 

1920 

Recurren-t 

CHART  XVI. 


19  I  8 
Incidence 

of 

Influenza 

b^  sex 

in 

Disfhcf^ 

3U  rve_^ec| 


Male  J 
Percent" 


Female  v^ 
Percent^ 


District 


1920 
Incidence 

Inf  luenzd 
^y  sex 
i  n. 
D  i  5t  r  ict^ 
-Surveyed 

.^ 

m 

m 

■ 

■ 

i 

m 

Male    1 
Percent" 

3.  9  8 

5.58 

9    1  1 

10    38 

1  1   27 

12.8^ 

8.  V6 

Female  ^ 
Percent  ^ 

6.57 

9.  M 

10.  77 

ID. ^2 

12.72 

1^.  Z5 

IQ.  23 

District 

Z 

6 

3 

1 

5 

^ 

All 
Districts 

Individ- 

ua  b 
Inaving 

Influenza 
in    both 

E|oidernics 
by   sey 

^mmrrmM 

^M 

^[///A 

MM 

■WJ 

■i^ 

Male     1 
Percent" 

0.51 

1.83 

1.51 

2A1 

3.  1  6 

4.  28 

2.D  8 

Female  vn 
Percent^ 

0.88 

1.76 

3.27 

3.3  3 

^.20 

3.  13 

2.70 

District 

2 

6 

3 

1 

5 

4 

All 
Di5tricf5 

AN    EPIDEMIOLOGIC    STUDY  143 

tricts  IV  and  V.  Districts  I,  II  and  III  were  in  the  tenement  section 
of  the  city,  while  District  VI  was  in  one  of  the  finest  residential  parts 
of  Brookline.  Districts  IV  and  V  were  midway  between  these  two  ex- 
tremes as  regards  economic  and  sanitary  status,  as  well  as  extent  of 
crowding.  The  lowest  incidence  was  in  the  Irish  tenement  district. 
The  highest  in  a  middle  class  Jewish  population. 

In  the  1920  recurrence  we  found  that  9.55  per  cent.,  or  one-tenth  of 
the  entire  population,  suffered  from  the  disease,  and  the  arrangement 
of  districts  in  order  of  incidence  was  very  little  changed.  The  Irish 
community  suffered  least;  the  two  middle  class  communities  most. 
The  well-to-do  district  in  Brookhne  had  the  next  lowest  incidence  in 
1920.  That  the  high  recorded  incidence  in  middle  class  districts  was 
not  due  to  more  accurate  or  more  thorough  work  on  the  part  of  the 
inspectors  is  indicated  by  the  fact  that  a  great  part  of  the  work  on 
Districts  IV  and  V  was  done  by  the  same  individuals  who  inspected 
Districts  II  and  III. 

One-fifth  of  the  population  studied  developed  the  influenza  in 
1918-19,  and  one-tenth  of  the  same  population  suffered  in  1920. 

We  may  agree  with  Winslow  and  Rogers,  who  conclude  that  the 
proportion  of  the  population  actually  affected  b}'  the  influenza  epi- 
demic in  1918  varied  between  200  and  400  per  thousand. 

Relation  of  sex  to  morbidity. — Abbott  concluded  from  his  studies  in 
1890,  that  the  weight  of  testimony  appears  to  favor  the  statement  that 
persons  of  the  male  sex  were  attacked  in  greater  number  and  with 
greater  severity  than  females.  Leichtenstern  reached  similar  con- 
clusions. In  the  epidemic  of  1889,  the  males  were  attacked  more 
frequently  than  the  females.  He  attributes  this  to  two  causes:  first, 
the  greater  exposure  to  infection,  and;  second,  the  fact  that  strong, 
robust  individuals  are  more  frequently  attacked. 

It  is  amusing  to  compare  this  explanation  with  another  found  in  the 
Medical  Supplement  to  the  Review  of  the  Foreign  Press  for  March, 
1919.  "A  Spanish  mission  composed  of  Maranon,  Pittaluga  and 
Falco  visited  Paris  last  October  to  collect  information  as  to  the  identity 
of  the  Spanish  epidemic  with  the  world  pandemic  of  influenza.  They 
found  that  the  epidemics  in  France  and  Spain  were  absolutely  identical 
from  the  epidemiologic,  bacteriologic  and  cHnical  standpoint.  The 
great  majority  of  the  severe  cases  in  both  countries  occurred  between 
the  ages  of  16  and  40.  Both  in  France  and  Spain  more  females  than 
males  were  attacked,  which  was  possibly  explained  by  the  greater 
tendency  of  the  former  to  lead  an  indoor  existence." 

Jordan,  Reed  and  Fink,  working  in  Chicago,  found  ver\'  different 


144  INFLUENZA 

results.  They  could  discover  no  noteworthy  difference  among  the 
pupils  in  high  school  and  elementary  school.  The  attack  rate  was 
230  for  the  boys  and  231  for  girls.  One  sex  was  presumably  as  much 
exposed  as  the  other. 

Among  the  employees  of  the  Chicago  Telephone  Company,  on  the 
other  hand,  the  men  were  affected  in  considerably  lighter  proportion 
than  the  women  (151  per  1,000  as  compared  with  233  per  1,000  for 
women).  Jordan  believes  that  the  age  factor  was  largely  responsible 
for  the  difference  as  the  women  employees  are  as  a  rule  of  much  lower 
average  age  than  the  men. 

Frost  found  that  with  few  exceptions  the  attack  rate  at  all  ages 
was  somewhat  higher  in  females  than  in  males.  The  total  excess  of 
incidence  in  females  was  six  per  cent.,  which  ranged  from  an  excess 
of  nineteen  per  cent,  in  the  highest  locality  to  a  deficiency  of  two  per 
cent,  in  the  lowest.  Only  two  of  the  eleven  localities  surveyed  showed 
a  lower  incidence  among  females  than  among  males. 

When  the  sexes  were  compared  in  different  age  groups,  the  female 
was  found  to  be  higher  than  the  male  in  each  age  period  except  under 
5,  10  to  14,  40  to  44,  and  70  to  74.  The  excess  of  incidence  in  males  in 
these  groups  is  relatively  small,  and  is  hardly  significant  in  the  highest 
age  groups,  where  the  rates  are  computed  from  small  figures.  Frost 
found  the  most  striking  excess  of  incidence  in  females  occurring 
between  the  ages  of  fifteen  and  forty,  the  difference  between  the  sexes 
being  relatively  slight  in  age  periods  above  and  below  these  limits. 
Females  over  the  age  of  fifteen  and  especially  between  the  ages  of  15 
and  45  were  either  more  susceptible  to  infection,  or  more  generally 
and  more  intimately  exposed  than  males  of  corresponding  age. 

Our  own  records  by  the  different  age  groups  were  remarkably 
similar.  We  have  found  an  excess  among  the  females  in  every  age 
except  under  five  years,  10  to  14,  50  to  54,  and  60  to  64.  In  1920  we 
found  a  slight  excess  among  the  males  up  to  the  age  of  15,  and  again 
at  the  ages  55  to  65.  Females  predominated  in  all  other  ages  (Chart , 
XVII).  Among  those  individuals  who  had  attacks  of  influenza 
during  both  epidemics  females  again  predominated  except  in  the  ages 
under  5  years,  10  to  14  and  55  to  59.  In  our  own  results  we  find  that 
ages  above  65  show  a  predominance  of  females. 

After  considering  both  series  of  results  it  is  safe  to  generalize 
in  saying  that  above  the  age  of  15'  the  female  sex  tends  to  acquire  the 
disease  in  slightly  greater  proportion  than  the  male  sex. 

Chart  XV  shows  the  predominance  of  the  female  incidence  in  both 
epidemics. 


CHART  XVll. 


JS^ 

10 

l^ss 

■■^10  cr 

o 
d 

IT)  in 

In 

fi 
^ 

s 

■■^O  T 

^^^■m  n 

■■■■iTl 
^■^■W   CM 

o 

o 
o 

^^Hiri 

CD 

^1'-' 

lO 

m 

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D 

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c  — 

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a   a    (D    cn 
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CD 
< 

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o 

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in 
io 

KXn'^ 

ih  01 
in  ifi 

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io 

Oi 

b:;:^^^ 

In  01 

o 

0 

b^^^^^^ 

in 

CD 

0 

ti^^^^^ 

In  in 

10  1^ 

o 

t^^^^^^ 

10  10 

o 

o 

In  01 

<= 

S 

■■■■■■H 

^^^^■1^^ 

a  T 

lO 

(^ 

to  01 

in 

T 

LWWvv^ 

■■■1 

a  T 

in 

5 

^^^^^ 

in  w 

s 

L:::^^^^^^ 

E   Si 
in  jj- 

a 

s 

t^ 

Si 

CO 

o6 

10 
10 
0 

c:    1   re  Q   o  (u   n 

^22  3  ^^^ 

< 

Q)  C 

Do 

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D. 

rot. 

CHART  XVIII. 


Distrib- 
ution 

of  192  Q 
cases 

accord- 
I  ng  to 

5everit_y 


Male 
Percent 


.ill. 


jzzzlW^ 


Female 
Percent 


4M6 


20.83 


2-=!. 76 


Miid 


Average 


Severe 


Pneumonia 


severe 
Pneurponia 
anc|  Fa  fa  I 


F'ercent 


Z28Z  ^3.23 


1918       |93Q 
Mild 


in    1320 

distnb-  H  H 

as  H  H  H  ■  H 

compared  H  H  ■  H  H 

with  1918  ^O  HI  H  1^ 

3iyiiiM.li 


3-1.^7    33. 7S 


35-.29    1771 


1918        1320 

Average 


|9ia       1920 

-5  evere 


7.^\    S.31 


I9ia      1320 

PneumonK 


^2.70  23D2 


/Average 
-Seventh 


CHART  XIX. 


District  1 

Influenza 
1918-19 

Case  Ra+e 
joer    IQO 
persons 
by  age 

joeriods 

■ 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

Age      ;^ 

15  mo 

5- 
3 

10- 
1^ 

IS- 
IS 

20- 
1^ 

25- 
29 

30- 
3^ 

35- 
33 

40-|45- 

30- 
5^ 

55-  '  60-!  65 
59   i64   1    -t- 

Percent 

5.88 

11.91 

155-^ 

II  51 

17  86 

3158 

2727 

21  32  2370 

i 

^542  21  05  16  66 

13.51 

M  28  a.3a 

District  2 

Influenza 
1918-19 

Cdse  Ra+e 
per    100 
persons 
D^    age 
periods 

1 

1 

1 

- 

1 

i 

1 

1 

1 — 

1 

1 

1 

-- 

1 

- 

1 

1 

1 

1 



1 

Age 

Ota 

\5mo 

l5mo 

3- 
3 

10- 
M 

15-- 
13 

20- 

2^ 

25- 
23 

30- 

3-=? 

35- 
33 

^5- 
^9 

50- 
5^ 

55- 
59 

60- 
64 

65 

Percent 

6-66J22.78 

27Q7 

H-D-l 

II3D 

1986 

15-82 

2^60 

ZC  14 

20.63 

6-.82 

9.03 

806 

3.77 

5.4  ( 

District  3 
Infljjenza 

19  18-19 


Ca^e  Ra+e 
joer    100 
'persons 

qy    age 

periods 


Age. 


Percent  ^3726.8221.73  13.16  /3  51 16  93  27.5821  2625  17  17  51  /O  00  10  66/2  €Z,)2  5016  06 


12 


CHART  XIX.—{Cont.) 


District^ 
Influenza 

1918-19 

Case  Rate 
per    100 
persons 
by  ag  e 
periods 


Age 


Oto 

l5mo 


Percent 


Di5trict5 
Influenza 

1918-19 

(ase  raj-e 
per    100 
per-sons 
by  age 
periods 

1 

Ibmo 

1 

i)- 
3 

1 

lo- 
ll 

1 

13 

1 

20- 
2^ 

1 

25- 
23 

1 

30- 
3^ 

1 

3  5- 
33 

1 

1 

A5- 
A9 

1 

50- 
SA 

1 

55- 
59 

1 

60- 
64 

65 

-t- . 

Ag& 

Oto 
15  mo 

Percent 

11.11 

"=13.73 

28.58 

25.99 

20.B3 

Z2.5I 

32.75 

3;.  1 6 

24.  II 

Z8.4I 

25.53 

15.72 

16.67 

2S.56 

3.70 

Distncf  B 

Influenza 

1918-19 

Case  rate 
per    100 
persons 
bjy  age 
periods 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 

Age 

DtD 

15m  0 

i5fno 

3- 

3 

10- 
1-1 

IS- 
IS 

20- 
2^ 

Z5- 
29 

30- 
3A 

25- 
33 

^0- 
AA 

A5- 
A9 

30- 
5A 

3--S- 
53 

80- 
6^ 

65 

-1- 

Percent 

1558 

24  6  Z 

30.^8 

.?9.63 

26.51 

15.5/ 

2  695 

29.36 

18.63 

11.63 

IZ.75 

8.9  7 

■^.ga 

11.86 

5-2  6 

CHAllT  XX. 


District  1 

Influenza 
I9I8-I3 

Cose.  Rate 
per    100 
per-sons 
bj     ^ex 
and  age 


Age 

fVTaTe  i 
F'ercentl 
Female.  I 
Percent  I 


District  2 

Influenza 

1918-19 
Ca5e  Rale 
per    100 
persons 
b^    .sex 
and  age 


Age 


Ma  le    ■ 
Percenf  ■ 


Fema  |e  ^ 

Percent.^ 


Districts 

Influenza 

19  18-19 
CdseRcite 
per    100 
persons 
by    sex 
and  d^e 


Age 


0  tDl5nio    3- 


10- 


15-     2  0 
19      21 


2  5     3D-    35-j  -=fO-    ^5-     5D-    55-    6  0-    6  5 
;29     31    39^4    ^9     -51     -5.9     61      j- 


Vaie 
■^6  ''ceni 


;  a.002GaO  19  25/771  5^5  9  I7    23.5520  5'i  2a79  I"?  c3  )0  00  II  76  1.51  625  7.11 


°.t     % 


12.50  26S2  25.00  S  10  22.22  2577  3/ 16  285729 73  2 1  BZ  10  00  12.902353  18  75  5  2C 


CHART  XX.— {Cord.) 


Dislricf^ 

Influenza 
19  18-19 

Case  "Ra+e 
per    iQQ 
persons 
by    sex 
and  oge 


I 


t 


Age 


0  to 
5mo 


(5  mo 


30- 
3^ 


35- 
39 


'=1-1 


4S-- 
■^9 


50- 
5^ 


55- 
S9 


5  0- 
61_ 


65 


Male     ■ 
Percent    I 


Fema  le 
PercehT 


Districts 
In-fluenza 

19  18-13 
Case  rate 
per   100 
per-sons 
b\j  ^ex 
dnd  age 


V7\ 


i 


I 


I 


I 


Age 


Q  to 

I  5  mo 


iSmo 


35- 

39 


^5- 
^9 


50- 
5^ 


5  5- 
59 


60- 
6-1 


65- 


Male    I 
Percent   " 


769 


5^.-^3 


2632 


iJ.33 


23.'2I 


29  11 


le  m  a  I  e    l 
Perceni"! 


16.67 


30.45  28.74 


22.11 


36.1-1 


294 


6.67 


Districts 
Influenza 

318-13 

Case  rate 
|oer     100 
joer  3ons 
hy    sex 
and  age 


F7 


i 


^ 


Age 


0  to 
l5mo 


ISmo 


Male 
Percent 


1 


30- 
3^ 


35- 
33 


^5- 
■^9 


50- 
54 


55- 
S5 


6  0- 
64 


55 

-t- 


2174    5  3£ 


Female 
Percent 


2941   ISl8 


CHART  XXI. 


Districtl 
Influenza 

1920 

Case  Ra+e 

per    100 

[Der^ons 

by  ag  e 

periods 

1 

I 

--- 

..     . . 

1 

1 

1 

1 

1 

1 

1 

1 

1 

1 



/^ge 

0  to 
ISmo 

l5mo 

sr- 
9 

10- 

IS- 
IS 

2  0- 
2^ 

25- 
^3 

30- 
3^ 

35- 

33 

-10- 

15- 
^9 

50- 

55 

59 

60- 
64 

65- 

t 

Percent 

840 

6  53 

4  73 

4   76 

12  50 

3'2\ 

17.58 

16  31 

II  .1  1 

19^9 

H  01 

^500 

10  ei 

M26 

4  65 

DistrictZ 

Influenza 

1920 

(ase  Ra+e 

per    lOQ 

persons 

by    cige 

periods 

1 

1 

_ 

, 

J 

1 

I 

1 

1 

I 

^ 

Age 

D  to 

l5ma 

s- 

)0- 

IS- 

20- 

j?5 

30- 

35- 

40- 

4  5^- 

5  0- 

55- 

60- 

&5 

I5ma 

'^yrs 

.3 

M 

13 

24 

23 

34 

33 

44 

49 

54 

53 

&4 

+ 

Percent 

6.0  6 

io.7e 

369 

3.35 

J?.2  6 

4.96 

4.52 

g.5z 

535 

7.14 

6  06 

5.6  8 

3.1% 

3.7  7 

2.70 

Disiricf  3 

Influenza 
1920 

Cc35e  'Ro\e 
per   iOO 
peT-sons 
b_y   a^e 
JDeriocJs 


CHART  XXL—{Cont. 


district  ^ 
Influenza 

1920 

Case-Ra+e 
per  100 
persons 
by  age 
periods 


/\ge 


Jjliil 

0  to    iBma     5         10-      \5~      20-     25-     30- 
iSfTiO^ji-^     3  M        }3       2-^        23       3^ 

S57   /3.33  3  5^  (D  2D  1^.2  8  SaS-^l    I5  l-=)    |7  M    /; 


lilill. 


5-^ 


55- 
33 


BO- 
54 


65 
-f- 


Percent    557 


3  5^ 


1^.28 


saa-^i 


;5"i5' 


J4Z8 


15  73 


^  4/ 


DistricfS 
Influenza 

19^0 

(cfse  rqte 
[oer    100 
[Der^ons 
b^y   age 
periods 


Age 


Percenf 


I 


Q  to 
l5mo 


ll.ll 


13.73 


11-73 


9.  0-1 


1325 


liiiUiiliki 

l5mo     S-      10-     15-     20-    25-    30-     35"-   ^=10-    45-    50-    S5- 
•=ix(r^    5        1^        19       Z^     29      3A      33     -^A     ^3     5^     S3 


.12,39 


moo 


10.87 


S.Z.^ 


6D- 
000 


I 


ll.ll 


Di5tric+  6 

Influenzct 

1920 

case  rate 
per   100 
persons 
b^/    age 
periods 


Age 
Percent 


15.3  8 


l5mo 
10-77 


5- 
15.85 


5-     20-    25-    3D 


liLjLLiltiLiL. 

DtO  l5mo     S-      ID-     15-     20-    25-    3D-    3S-    -^D-    -^5- ,50-  SS-     BD-    65 
5mo  4sr^    .3         M       13       2^      29     34     39     4^      49      5^     53       6-1       -j- 


6.17    9.6-1    73-1  Ls: 67 


5.86 


3.33 


2.63 


AN    EPIDEMIOLOGIC    STUDY  145 

Relationship  of  sex  to  severity. — In  classifying  cases  as  to  severity, 
we  have  followed  the  standard  previously  described.  Our  results 
have  shown  that  the  1920  recurrence  in  our  group  of  individuals  has 
been  decidedly  milder  than  the  earlier  1918  spread.  The  proportion 
of  mild  cases  in  1920  is  nearly  twice  that  of  mild  attacks  in  1918-19. 
The  proportion  of  severe  cases  was  twice  as  great  in  1918  as  in  1920. 
The  actual  severity  in  1918  was  even  greater  than  would  be  indicated 
by  these  figures.  The  last  column  in  Chart  XVIII  is  a  combination 
of  the  two  preceding,  and  while  the  1920  column  includes  all  classed 
as  severe,  pneumonia,  and  fatal,  that  for  1918  only  includes  the  severe 
and  pneumonia  cases,  but  does  not  include  the  fatal  cases  for  that 
year,  because  those  who  died  during  the  1918-19  epidemics  are  not 
counted  in  our  10,000  individuals  surveyed.  If  these  were  included 
the  percentage  of  total  severe,  or  average  severity  would  be  greater 
than  42.70. 

We  find  that  in  1918  the  female  sex  had  a  higher  proportion  of 
severe  cases  according  to  our  standard  than  did  the  male.  This  was 
equally  true  in  1920.  We  should  emphasize  here  that  we  are  not  com- 
paring only  the  fatal  cases  in  the  two  sexes,  but  all  classified  as  severe, 
and  including  fatal  in  1920. 

Not  only  was  the  female  sex  attacked  in  slightly  greater  proportion, 
but  also  the  individual  cases  appear  to  have  been  on  the  aggregate 
somewhat  more  severe  in  that  sex. 

Morbidity  by  age. — Before  discussing  the  incidence  of  influenza  in 
the  various  age  periods  we  should  explain  that  the  charts  for  1920  are 
based  on  the  ages  given  by  the  individuals,  and  those  for  1918  upon 
these  ages,  corrected  by  the  subtraction  of  15  months  from  the  age  as 
given.  In  our  study  of  cases  recurring  during  both  epidemics  the  age 
used  in  the  calculations  is  that  of  1920.  It  is  for  this  reason  that  in 
aU  of  our  age  charts  we  have  a  first  age  period  from  zero  to  15  months. 
Infants  of  less  than  15  months  at  the  time  of  our  survey  were  born 
subsequent  to  the  peak  of  the  1918-19  epidemic,  and  are  not  included 
in  computations  for  that  time. 

The  general  similarity  of  the  age-incidence  in  the  six  districts 
studied  (Charts  XIX  and  XX)  is  evident.  As  a  rule  two  peaks  can 
be  discerned,  one  falling  somewhere  between  15  months  and  9  years, 
and  the  other  between  20  and  39  years.  There  are  individual  varia- 
tions in  the  different  districts,  and  in  Districts  IV,  V  and  VI  there  is  a 
tendency  toward  a  peak  in  the  period  55  to  64.  This,  however,  disap- 
pears when  the  total  10,000  is  tabulated,  when  the  two  peaks,  15 
months  to  9  years,  and  20  to  39,  show  out  clearly  for  the  year  1918 
(Chart  XVII). 


146  INFLUENZA 

Frost  found  for  the  same  epidemic  that  the  attack  rate  was  highest 
in  the  age  group  5  to  9,  decHning  with  almost  unbroken  regularity  in 
each  successive  higher  age  group,  with  the  exception  of  the  groups  25 
to  34,  in  which  the  attack  rates  were  higher  than  in  the  age  groups  15 
to  24,  but  not  as  high  as  that  of  5  to  9. 

Both  series  of  observations  agree  in  finding  relatively  high  incidence 
in  early  childhood  and  in  early  adult  life. 

For  1920  (Chart  XVII)  we  find  that  these  peaks,  although  present, 
have  become  decidedly  less  prominent,  and  that  there  is  a  relatively 
higher  incidence  in  individuals  past  the  age  of  40  (Charts  XXI  and 
XXII).  There  is  some  tendency  toward  straightening  out  of  the 
curve;  age  appears  to  have  played  a  less  important  part,  and  those 
higher  ages  which  were  relatively  insusceptible  in  1918  have  become 
more  susceptible  in  1920.  We  cannot  generahze  in  the  statement  that 
all  ages  which  were  Hghtly  attacked  in  the  first  epidemic  were  more 
severely  attacked  in  the  1920  spread,  because  the  ages  from  10  to  19 
are  found  to  be  relatively  lower  during  both  epidemics. 

Other  observations  have  been  made  regarding  the  age  incidence 
particularly  during  the  1918  pandemic.  Jordan's  figures  for  the 
October  epidemic  show  a  higher  incidence  among  school  children  of 
ages  4-13  than  among  those  of  higher  school  age,  14-18.  The  teachers 
in  these  schools  had  a  lower  attack  rate  than  the  pupils.  The  pupils 
in  both  school  groups  were  from  the  same  section  of  the  city  and  to  a 
large  extent  from  the  same  famihes  and  were  presumably  exposed  in 
similar  degree. 

Lynch  and  Cumming  found  that  of  49,140  children  in  pubhc  institu- 
tions the  influenza  rate  was  412  per  1,000,  while  among  703,006  adults 
in  similar  institutions  the  rate  was  263  per  1,000.  These  figures 
include  children  in  a  large  number  of  institutions  scattered  throughout 
the  United  States,  and  would  indicate  that  in  childhood  the  suscepti- 
bility is  much  greater  than  in  adults. 

Many  writers  agree  that  nursing  infants  show  a  relative  insuscepti- 
bihty.  However  Abt  records  a  case  of  an  expectant  mother  who,  with- 
in two  weeks  of  term,  developed  influenza,  and  during  the  course  of 
her  illness  gave  birth  to  a  baby  boy,  who  at  birth  was  found  to  be 
suffering  from  bronchitis  and  bronchopneumonia,  but  who  lived  for 
three  days,  finally  dying  of  bronchopneumonia.  Abt  concludes  from 
a  review  of  all  of  the  facts  that  the  newly  born  infant  had  influenza 
and  that  the  baby  had  become  infected  before  birth. 

According  to  Carnwath,  the  age  incidence  showed  curious  changes. 
During  the  1918  summer  wave  the  ages  most  affected  w'ere  15  to  45. 


CHAR'l'  XXII. 


District  1 

Inf  luenza 
1920 

Case  Rate 

per  100 

persons 

b_y    sex 

and  age 


i 


m 


tk 


%A 


m 

20-    Q5- 

24     29 


I 

35- 
39 


55-    60- 
5^9      6  4 


i 


/Age 


0  to 

l5nio 


l5mo 
4jr-s 


10- 


30- 
34 


40- 

14 


Mole      ■ 
Percen-h  B 


833 


6  35 


5.83 


12.16 


1642 


17  14  28  56 


1364 


4.76 


Fe  m  a  I  e    1 
Percent  I 


847 


672 


52  6 


3  73 


1098 


2262 


19.35 


984 


9.03  20.UO 


6.6  7 


10  00 


9.09 


District  2 

Influenza 
1920 

(ase  F?ate 
per    100 
persons 
b^y    .sex 
and  age 


h 


I 


i^ 


la 


^kn. 


ik 


I 


J 


J 


fe 


/\ge 


Oto 
ISmo 


15  mo 
4jr.s 


20-     2  5- 

24  !    23 


30- 
34 


35- 
33 


'IS-      50-  I    S5- 

13   !    S-t    i     53 


50- 
64 


55 


Male        ■ 
PercenT  ■ 


763 


1268 


2  70 


526 


30S 


4  17     I  D7 


484    161      2.50    0.00:4  54    000 


Female 
Percenr 


3.70  I  9.20 


9,37    1000    833'555!323     S.\2. 


I]lSlTlct3 

Influenza 

1920 
Case  Rate 
|oer    100 
loersons 
b_y   sex 
dnci  age 


t 


i 


fe 


i 


I 


i 


J 


Age 


Oto  ISmo    5- 
!/5'Tio!-4-jr3|    g 


15-    2  0- 
19     24 


25    30-33-    'ID-'  45-    50-   55-  '  60-i  65 
Z3;34      ^9     '^^      -=f  3      54     59,64       -J- 

— i ^ , 1 : 


Pe 


^^1^    I     1^28:14  d5.46 


8.87 


545  456 


586)506 


13.04    3.-l5,Z.Q0  2  94  1563  l873   000 


Femo  le 
Percent 


3.371 13 ■»!    6  00 


504 


9  03  12  37 


16  85/2  69  13  50 U 0  31    1500  7  31    2553  16  75  0  00 


CHART  XXll.—iCont.) 


Influenza 
1920 

(dse  Rate 
per    100 
persons 
by  ^ex 
and  age 


I 


m 


L 


i 


I 


i 


I 


I 


IL 


Ase 


Ota 

15mo 


iSmo 


ID- 


15- 
19 


30- 
3^ 


3  5- 
33 


^5- 
^9 


S5- 
53 


6  0- 
6^ 


55 


Male         ■ 
Percent     ■ 


Female 
Percenl* 


District  5 
Inftuenzd 

1920 
(pse   rate 
|oer    100 
perjsons 
by    ^ex 
ancj  age 


llli 


il 

15-    20- 
13       24 


J 


J 


L 

55- 
59 


Age 


0  to 

IS'mo 


l5tno 


2  5- 
23 


30- 
3^ 


3  5- 
39 


40- 


4  5- 
^9 


SO- 
54 


60- 


65 


M  ale      ■ 
Percent  ■ 


12.82 


1646 


/4.9I 


667 


ie.07 


1519 


4.29 


5".  00 


4.V6 


Fe  male 
Percent 


8.70 


0.61 


District  0 

Influenza 

19  2  0 


Ca^e  rate 
foer    100 
■per-sons 
by    sex 
and  age 


I 

)5r7iQ 


m 


e 


i 


ii 


L 


M 


i 


.1^- 


Age 


0  to 
15mo 


IS- 
IS 


20- 
2^ 


30- 
3^ 


35- 
39 


^90- 
4-1 


45- 


50- 
51 


53 


50- 
64 


65 

-t- 


M  ale  ■ 

Percent  ■ 

Female  m 

Percent  H 


9.80 


^.41 


2.9  9 


AN    EPIDEMIOLOGIC    STUDY  147 

In  the  winter  of  1918-19  there  was  a  considerable  shifting  toward  the 
extremes  of  life  and  particularly  toward  the  younger  years.  The 
susceptibility  of  j'^oung  children  was  the  subject  of  a  special  inquiry  in 
London.  Though  the  attack  rate  was  below  the  average,  the  chances  of 
recovery  were  less  than  in  other  age  groups.  Of  breast-fed  infants, 
30  per  cent,  contracted  the  disease;  of  artificially-fed  54  per  cent.  The 
opposite,  however,  occurred  in  lying-in  homes.  An  inquiry  in  Cheshire 
revealed  that  25.4  per  cent,  of  expectnnt  mothers  affected  died. 

Renon  and  Mignot  have  made  a  report  on  the  1920  recurrence. 
According  to  them  the  grip  of  1920  attacked  all  ages,  in  contradis- 
tinction to  the  1918  epidemic,  which  attacked  especially  the  young 
and  vigorous.  One-third  of  their  group  were  over  40  years  of  age, 
while  some  were  70  and  80  3'ears  old.  In  spite  of  this  the. disease 
remained  relatively  mild. 

Age  morbidity  in  previous  epidemics. — Previous  to  the  epidemic  of 
1889-93,  the  various  recorded  observations  regarding  morbidity,  and 
particularly  regarding  age  morbidity,  have  consisted  often  of  records 
made  by  practising  physicians,  and  are  merely  estimates  based  upon 
their  clinical  experience  and  varying  with  the  type  of  individual 
treated  by  them.  Or  else  they  have  been  records  made  by  non-medical 
historians.  During  the  19th  century,  the  tendency  toward  statistical 
enumeration  becomes  more  and  more  prominent,  but  the  first  statis- 
tical studies  of  real  value  to  the  epidemiologist  were  made  in  the  epi- 
demic of  thirty  years  ago.  Statistical  study  must  begin  with  this  last 
epidemic.  Observations  of  the  earher  epidemics,  while  very  inter- 
esting for  reference  and  comparison,  are  no  longer  acceptable  as 
unquestioned  statements  of  fact.  Even  at  the  present  time  and  with  all 
of  the  emphasis  that  is  now  being  laid  upon  statistical  procedure  the 
records  are  far  from  perfect,  and  it  is  to  be  hoped  that  in  years  to  come 
the  improvement  wiU  be  so  decided  that  the  records  even  of  the  1918-20 
epidemics  will  appear  crude. 

Buoninsegni  remarks  of  the  1387  epidemic  that  many  individuals  of 
all  ages  died,  but  the  deaths  were  particularly  prevalent  among  the 
aged. 

Jacob,  of  Konigshofen,  writes  that  "there  came  a  general  pestilence 
in  the  whole  country,  with  cough  and  influenza,  so  that  hardly  one 
among  ten  remained  healthy,"  and  that  old  and  debilitated  persons 
were  frequently  the  victims. 

BaKoanus  tells  us  that  the  epidemic  of  1404  let  not  rank,  age  nor 
sex  escape  its  effect. 

In  1557, according  to  Valleriola,  the  disease  appeared  with  pesti- 
lential rapidity,  and  spared  neither  sex,  nor  any  age,  nor  rank,  neither 


148  INFLUENZA 

children  nor  old  persons,  rich  nor  poor,  but  that  it  was  not  as  a  general 
rule  dangerous;  children  only,  who  could  not  freely  cough  out  the 
phlegm,  dying. 

The  same  story  is  told  by  Molineux,  for  1693,  "All  conditions  of 
persons  were  attacked,  those  residing  in  the  country  as  well  as  those  in 
the  city;  those  who  lived  in  the  fresh  air  and  those  who  kept  to  their 
rooms;  those  who  were  very  strong  and  hardy  were  taken  in  the  same 
manner  as  the  weak  and  spoiled;  men,  women  and  children,  persons  of 
all  ranks  and  stations  in  life,  the  youngest  as  well  as  the  oldest." 
Molineux,  however,  added  that,  ''it  rather  favored  the  very  old  who 
seldom  were  attacked  with  it." 

These  observations  are  but  broad  generalizations;  if  we  pause  to 
study  the  psychology  of  the  historian  we  are  tempted  to  conclude  that 
his  primary  object  was  to  impress  his  readers  with  an  idea  of  the  enor- 
mousness  of  the  dissemination  of  the  disease  during  his  period.  That 
being  the  main  endeavor,  a  tendency  to  exaggerate  for  the  sake  of 
rhetoric  and  yet  remain  within  the  limits  of  truth  may  be  considered 
excusable.  But  during  the  1889-93  epidemic  there  was  ample  oppor- 
tunity to  compare  the  estimates  made  by  the  practising  physicians 
with  the  later  statistical  tabulations.  As  a  rule  the  former  were 
higher  both  as  regards  morbidity  and  mortality. 

In  the  1830-32  epidemic  an  interesting  observation  has  been  made. 
While  Kahlert  says  that  no  distinction  between  age,  sex  nor  rank 
occurred,  Leberscht  stated  that  persons  of  middle  age,  especially  women 
in  the  climacteric  period,  were  attacked  with  special  frequency.  This 
is  of  interest  in  view  of  the  findings  in  the  1918  epidemic.  Krimer 
states  for  the  same  epidemic  that  children  under  14  years  of  age  and 
adults  over  45  years  were  spared  by  the  epidemic. 

For  the  1836-37  epidemic  Finkler  records  the  following:  "Most  of 
the  patients  were  adults  from  20  to  40  years  of  age,  and  of  these  more 
women  than  men  were  attacked.  Curiously,  however,  the  physicians 
of  Wiirtenberg  speak  of  the  great  dissemination  of  the  disease  among 
children." 

In  1847-48,  among  the  adult  influenza  patients,  there  are  said  to 
have  been  more  women  than  men.  According  to  Canstatt,  there  were 
proportionately  more  children  than  adults  attacked. 

In  1889-90,  according  to  Finkler,  no  age  was  spared,  but  persons 
between  20  and  50  years  of  age  were  attacked  by  preference.  No 
trade  was  a  sure  protection.  The  course  of  the  disease  in  general  was 
favorable  and  also  quite  rapid,  unfavorable  only  in  many  children 
during  the  first  few  years  of  life,  in  many  old  people,  in  many  de- 
bilitated persons,  and  especially  in  those  suffering  from  chest  affections. 


AN    EPIDEMIOLOGIC    STUDY  149 

An  interesting  table  of  this  kind  is  given  us  by  Leichtenstern. 
His  hospital  material  included  439  influenza  patients,  and  these  he 
carefully  grouped  according  to  age. 

Age.  Influenza  General 

admissions,         average  of 
per  cent.  admissions, 

per    cent. 

Under  10  years 0.9  0.7 

10-20  years 14.7  8.8 

20-30  years 40.3  27.5 

30-40  years 19.1  23.3 

40-50  years 10.1  15.7 

50-60  years 7.4  12.3 

60-70  years 5.3  8.9 

70-80  years 1.7  2.6 

Above  80  years 0.4  0.2 

Comby  found  that  in  Paris  only  the  new-born  were  noticeably  insus- 
ceptible to  influenza,  that  children  up  to  15  years  were  attacked  in  the 
proportion  of  40  per  cent.,  and  adults  in  the  proportion  of  60  per  cent. 
Danchez  believed  that  in  families  in  which  all  the  adults  became  ill,  the 
little  children  usually  escaped. 

Finkler  states  that  in  the  schools  at  Bordeaux  the  older  children 
were  first  and  most  frequently  attacked.  Of  the  248  male  and  female 
teachers  in  41  schools,  153  (61.7  per  cent.)  developed  the  disease. 
Children  up  to  five  or  six  years  of  age  at  any  rate  seem  to  have  been 
very  little  affected,  while  older  children  were  no  less  susceptible  than 
adults. 

Among  47,000  cases  of  influenza  treated  by  physicians  in  Bavaria 
in  1889,  the  various  ages  were  as  follows: 

1  year                       2-5                       6-10                     11-15                    16-20  21-30 

1.5  per  cent.  5.4  per  cent.  6.6  per  cent.  7.2  per  cent.  11.4  per  cent.  22.2  per  cent. 

31-40                      41-50                    51-60                    61-70                   71-80  Above  80 

19.3  per  cent.  12.6  per  cent.  7.7  per  cent.  3.6  per  cent.  2.0  per  cent.  0.5  per  cent 

Leubuscher  recorded  that  in  Jena  the  proportion  of  cases  in  the 
individual  age  classes  did  not  correspond  with  the  figures  reported 
from  other  localities.  Children,  and  especially  very  young  children, 
suffered  relatively  less  than  adults. 

The  following  statistics  of  the  1889-90  incidence  of  influenza 
among  school  children  in  Cologne  were  collected  by  Lent : 

Attendance.  HI  of  influenza. 

Class     1—13  to  14  years  of  age 3,002  1,015  33 . 8  per  cent.  \ 

Class    II — 11  to  12  j^ears  of  age 5,737  1,835  31 .9  per  cent. 

Class  III— 10  years  of  age 3,701  1,130  30.5  per  cent. 

Class  IV—  9  years  of  age 3,590  930  25.9  per  cent. 

Class    V—  8  j-ears  of  age 2,929  822  28.0  per  cent. 

Class  VI —  7  years  of  age 3,388  758  22 . 3  per  cent. 


150  -  INFLUENZA 

These  may  be  compared  with  figures  for  the  pubHc  schools  in  the 
suburbs  of  Cologne : 

Attendance.  Ill  of  influenza. 

Class     I— 13  to  14  years  of  age 1,609  689  42.9  per  cent. 

Class    II— 11  to  12  years  of  age 2,885  1,094  37.9  per  cent. 

Class  III— 10  years  of  age 1,683  626  37 . 1  per  cent. 

Class  IV —  9  years  of  age 1,758  552  31 .4  per  cent. 

Class    V—  8  years  of  age 1,771  502  28.2  per  cent. 

Class  VI—  7  years  of  age 1,938  510  26.3  per  cent. 

The  increase  of  disease  incidence  with  age  is  apparent.  Finkler's 
explanation  for  the  higher  incidence  among  the  children  of  the  sub- 
urbs, "that  the  children  in  the  country  had  usually  to  walk  a  greater 
distance  to  school"  does  not  appear  to  be  complete. 

Comby  found  that  out  of  3,411  school  children  in  Lausanne  1,840 
contracted  influenza.  This  shows  a  relatively  high  incidence  in 
children  of  school  age  in  that  city. 

Concerning  age  distribution  in  1889-90  Leichtenstern  remarks  that 
the  greatest  morbidity  incidence  was  in  school  children,  adolescents 
and  young  adults,  especially  the  last.  Nursing  infants  were  attacked 
in  considerably  less  degree  than  any  of  these  other  ages.  Also  in  the 
higher  ages  those  above  sixty  were  attacked  in  lesser  degree.  The 
greatest  morbidity  frequently  was  between  the  ages  of  twenty  and 
forty.  Abbott  concluded  on  the  basis  of  estimates  furnished  him 
from  various  institutions  and  individuals  in  the  State  that  people  of 
all  ages  were  attacked  but  the  ratio  of  adults  was  greatest,  of  old 
people  next,  and  of  children  and  infants  least. 

Relationship  of  occupation  to  morbidity  incidence. — ^Leichtenstern 
found  that  the  only  apparent  influence  of  occupation  on  the  incidence 
of  influenza  depended  upon  the  liability  to  exposure  in  the  various 
occupations.  He  remarks  particularly  on  the  large  incidence  of 
influenza  among  physicians.  In  contrast  was  the  low  incidence  in 
lighthouse  keepers.  In  1889-90  among  415  dwellers  on  51  lightships 
and  20  isolated  lighthouses  on  the  English  coast  only  8  persons  de- 
veloped influenza  and  these  in  four  localities,  and  in  every  instance 
there  was  traceable  direct  communication  from  some  other  source. 
There  is  contradictory  evidence  as  to  whether  individuals  working  out 
of  doors  are  more  apt  to  develop  influenza.  Certain  statistics  show 
that  postmen  and  individuals  working  on  railroads  were  attacked  more 
frequently  and  earlier  than  others,  while  other  statistics  show  that 
in  railroads  the  office  personnel  was  attacked  earlier  than  individuals 
on  the  trains  and  those  working  on  the  tracks. 

Abbott  concluded  that  special  occupations  did  not  appear  to  have 
had  a  marked  effect  in  modifying  the  severity  of  the  epidemic.     At 


AN    EPIDEMIOLOGIC    STUDY  151 

the  Boston  Post  Office  in  1889-90,  of  the  indoor  employees,  475  in 
number,  25  per  cent,  were  attacked.  Of  the  carriers,  450  in  number, 
11  per  cent,  were  affected  with  the  disease.  But  there  were  other 
reports  of  the  same  period  which  stated  that  t^"  ratio  of  the  persons 
employed  at  outdoor  occupations  who  were  attacked  was  greater  than 
that  of  indoor  occupation. 

Finkler  has  discussed  the  influence  of  occupation  at  some  length: 
"When  we  compare  the  statistics  of  the  last  pandemic  concerning 
the  influence  of  vocation,  we  see  in  the  first  place  that  those  first  and 
chiefly  were  attacked  whose  occupation  compelled  them  to  remain  in 
the  open  air.  This  was  shown  especially  by  Neidhardt,  who  studied 
the  influenza  epidemic  in  the  Grand  Duchy  of  Hesse.  His  conclusions, 
however,  were  disputed  by  others.  Thus,  the  prejudicial  influence 
of  exposure  to  the  open  air  was  not  supported  by  the  statistics  of  rail- 
road employees  in  Saxony.  Of  those  who  were  employed  in  the  out- 
door service,  32  per  cent,  became  ill;  of  those  employed  in  office  work, 
on  the  other  hand,  40  per  cent.  The  statistics  of  the  local  benefit 
societies  in  Plauen  show  that  the  percentage  of  the  sick  among  farm 
hands  and  builders  was  not  greater  than  that  among  the  members 
of  other  benefit  societies  who  worked  indoors.  In  Schwarzenberg 
the  laborers  in  the  forest  who  were  working  in  the  open  air  all  day  were 
affected  less  than  others,  and  there  was  no  sickness  whatever  in  some 
forest  districts.  Lancereaux,  of  Paris,  states  that  most  of  the  railroad 
employees  who  suffered  from  influenza  were  those  engaged  in  office 
work  and  not  those  who  worked  in  the  open  air.  The  preponderance 
of  influenza  patients  among  the  factory  hands  may  be  seen  from  a  table 
prepared  by  Ripperger : 

A.  In  the  open  air. 

Occupation.  Per  cent. 

attacked. 

Workmen  and  laborers  of  Niederbayern 7 

Railway  officials  in  Amberg. 9 

Peasants  in  Niederbayern 11.7 

Workmen  in  the  Salzach-Correction 20 

B.  In  closed  rooms. 

Slag  mills  in  St.  Jugbert 15 

Cotton  mill  in  Bamberg 20 

Cotton  mill  in  Bayreuth 33 

Sugar  factory  in  Bayreuth 36 

Aniline  works  in  Ludwigshaf en 38 . 8 

Cotton  mill  in  Zweibrticken 50 

Tinware  factory  in  Amberg 60 

Factory  in  Schweinf urth 62 

Gun  factory  in  Amberg 70 

Gold  beaters  in  Stockach 80 


152  INFLUENZA 

"Many  peculiar  records  of  how  individual  classes  of  occupation 
have  fared  are  obviously  to  be  explained  by  the  fact  that  the  infection 
manifested  its  action  in  very  different  degrees.  Thus,  among  the 
workmen  on  the  Baltic  ship-canal  only  those  became  ill  who  lived  in 
the  town  of  Rendsburg;  those  who  had  been  housed  in  barracks  outside 
of  the  city  were  not  affected.  Of  the  438  lead  workers  of  Rockhope, 
which  is  situated  in  a  lonely  valley  in  Durham,  all  remained  perfectly 
free  from  the  disease  during  the  three  epidemics  of  1889-92. 

"Some  occupations  are  said  to  afford  protection  against  influenza. 
Thus  workmen  in  tanneries,  chloride  of  lime,  tar,  cement,  sulphuric 
acid,  glass,  and  coke  works,  are  said  to  have  escaped  the  disease  with 
extraordinary  frequency. 

"We  shall  be  compelled  perhaps  to  agree  with  Leichtenstern  in  his 
conclusion  that  occupation  and  social  position  only  in  so  far  exert  an 
influence  on  the  frequency  of  the  disease  as  certain  occupations  in  life 
lead  to  more  or  less  contact  with  travellers. 

"Very  remarkable  is  the  proportionately  small  number  of  soldiers 
affected,  at  least  in  the  Prussian  army,  where,  according  to  the  official 
record,  the  epidemic  from  its  beginning  to  its  end  attacked  only  101.5 
per  thousand  of  the  entire  forces. " 

Comparison  of  morbidity  by  occupation  necessarily  includes  so 
many  variables  and  so  many  factors  other  than  occupation  that  the 
results  are  decidedly  unsatisfactory.  An  example  is  found  in  Jordan, 
Reed  and  Fink's  report  of  the  incidence  among  troops  in  the  Student 
Army  Training  Camps  in  Chicago.  They  found  a  strikingly  different 
attack  rate  in  the  various  groups  studied.  In  the  Chicago  Telephone 
Exchange  they  ranged  from  30  to  270  per  1,000,  although  the  working 
conditions  in  the  various  exchanges  were  not  materially  different. 
In  the  Student  Army  Training  Corps  at  the  University  of  Chicago 
the  lowest  was  39  and  the  highest  398  per  1,000.  The  higher  rate 
group  was  particularly  exposed  to  infection  while  the  lower,  although 
composed  of  men  of  similar  ages,  living  under  similar  conditions,  were 
guarded  to  a  considerable  extent  against  contact  with  beginning 
cases. 

WooUey  has  made  an  interesting  observation  on  the  effect  of 
occupation:  "The  disease  was  no  respecter  of  persons  except  that  it 
was  more  severe  in  those  who  were  hard  workers.  Those  who  tried  to 
'buck  the  game'  and  'stay  with  it'  showed  the  highest  mortality 
rates.  So,  the  non-commissioned  officers  and  the  nurses  suffered 
more  severely  than  the  commissioned  officers  and  privates. 


AN    EPIDEMIOLOGIC    STUDY  153 

"The  annual  morbidity  rate  per  1,000  was  as  follows: 

For  commissioned  officers 261 

Non-commissioned  officers 208 

Nurses 416 

White  enlisted  men 568 

Black  enlisted  men 1,130 

"The  annual  mortality  rate  per  1,000  was: 

For  commissioned  officers 69 

Non-commissioned  officers 83 

Nurses 77 

White  enlisted  men 145 

Black  enlisted  men 253 

"The  case  mortalities  were: 

Per  cent. 

For  commissioned  officers 26.8 

Non-commissioned  officers 40 . 0 

Nurses 33.3 

White  enlisted  men 26 . 0 

Black  enlisted  men 22 . 5 

"The  above  figures  are  for  the  period  of  five  weeks  from  August 
28th  to  October  1st,  1918,  and  cover  the  most  active  portion  of  the 
epidemic,  but  are  obviously  incomplete.  They  are  given  for  purposes 
of  comparison." 

Woolley  makes  the  observation  that  the  organizations  which  spent 
most  of  the  time  in  the  open  and  which  were  therefore  most  exposed 
to  the  weather  suffered  least  during  the  epidemic.  This  was  particu- 
larly true  in  the  Remount  Depot. 

In  our  work  we  have  attempted  to  classify  our  population  according 
to  occupation  along  very  broad  lines. 

"Infant"  includes  all  individuals  up  to  the  age  of  two  years.  In 
these  the  exposure  is  hmited  by  the  fact  that  they  are  either  relatively 
isolated  at  home,  or  when  abroad,  are  still  under  relative  isolation  in  a 
perambulator  or  under  the  eye  of  a  nurse.  There  is  relatively  little 
commingling  with  the  older  age  groups. 

"Child"  refers  to  all  children  up  to  the  age  of  school  years.  There 
is  relatively  much  greater  commingling,  particularly  with  other  indi- 
viduals of  the  same  age. 

"School"  refers  to  all  children  and  adolescents  who  were  reported 
as  attending  school. 

"Home"  includes  not  onl}^  the  housewife,  the  housekeeper,  but  also 
servants  and  invalids;  all  who  in  their  daily  routine  spend  the  greater 
part  of  the  time  in  the  home. 

13 


154  INFLUENZA 

"Manual  Indoors"  refers  chiefly  to  laborers  in  factories  and 
includes  all  manufacturing  occupations  in  which  the  work  is  of  a 
manual  character  no  matter  what  the. particular  branch. 

"Manual  Outdoors"  refers  to  such  occupations  as  ditch  diggers, 
street  cleaners,  conductors  and  motormen,  longshoremen,  trucksters 
and  teamsters,  telephone  and  telegraph  linemen,  etc. 

"Retail  Sales  Indoors"  refers  to  clerks  in  stores  and  all  other 
individuals  who,  working  indoors,  come  into  about  the  same  degree  of 
contact  with  the  public-at-large. 

Retail  Sales  Outdoors"  includes  sales  agents,  life  insurance  agents, 
traveling  salesman,  pedlers,  newsboys,  etc. 

"Office,"  officials,  secretaries,  stenographers,  telephone  operators, 
telegraph  operators,  etc. 

We  have  observed  that  in  1918  infants  presented  the  lowest  inci- 
dence and  school  children  the  highest.  Occupations  desigiiated  Home 
and  Office  were  surprisingly  high.  Children  also  showed  a  high  inci- 
dence, one  out  of  every  five  developing  the  disease.  The  records  shov/ 
that  manual  labor,  both  indoors  and  outdoors,  was  associated  with  a 
higher  incidence  than  less  strenuous  work,  as  retail  sales,  indoors  and 
outdoors  (Chart  XXIII). 

The  attack  rates  in  most  of  the  occupations  are  so  nearly  the  same 
as  to  lead  to  no  certain  conclusions.  It  would  appear  from  our  records 
that  individuals  working  out  of  doors  were  less  frequently  attacked 
than  those  whose  occupation  kept  them  in  doors.  The  groups  at  the 
two  extremes  of  incidence  correspond  to  what  we  should  expect  when 
considering  opportunities  for  contract.  The  infant  has  least  direct 
contact.  His  contact  is  only  with  one  or  a  few  individuals,  the  mother 
or  the  nurse.  This  group  developed  the  disease  in  5.8  per  cent.  The 
school  child  not  only  has  the  same  degree  of  contact  as  do  adults,  but 
also  in  the  tussle  and  scramble  of  play  the  contact  becomes  much 
closer.  The  factor  of  age  plays  a  large  part  in  the  occupational  dis- 
tribution and  the  apparent  occupational  susceptibility  is  influenced 
by  the  age  susceptibihty. 

When  we  consider  the  occupational  incidence  in  the  various  dis- 
tricts we  find  that  the  only  constant  feature  in  the  relatively  small 
groups  is  the  low  incidence  among  infants  (Chart  XXIV). 

The  first  fact  gained  from  a  study  of  the  1920  occupational  case 
rate  is  that  just  as  was  the  case  in  age  incidence  there  is  less  variation 
between  the  highest  and  the  lowest  than  in  1918-19.  While  in  the  first 
epidemic  the  highest  occupational  rate  was  five  times  the  lowest,  in 
the  second  it  was  only  twice  the  lowest  (Chart  XXV).     But  at  the 


CHART  XXIII 

• 

Influenza 

1918-19 

Case,  ra^e 

— 

^ 

— 



per    100 

[aer^ans 

b^ 

^ 

Occujad- 

^ 

■ 

■ 

■ 

■ 

tion 

^ 

1 

1 

1 

1 

1 

1 

1 

1 

Percent 

5.77 

IDTl 

17,03 

1801 

13.51 

19  8  8 

ZD.I7 

2193 

23.27 

< 

\  W  I. 

1^ 

^ 
^ 

1 

I nf luenza 

1918-13 
Case  TRa+  e 

|oer 
loo  male 
joer^ons 
b^    occu- 

1 

1 

1 

1 

16.98 

1 

19,35 

20-09 

1 

20-23 

1 

25^1 

Percent 

5.39 

ID  13 

II. n 

16.20 

1 

^ 

5 

Influenza 

1918-19 

Case  T?a"te 

per   100 

female 

persons 

by  occu- 

|oq  +  ion 


v? 


Percent 


0  DO 

N    «)    ^ 

^1 


6.17 


I 


19.46 


20  M 


A. 

20.28 


.^ 


2267 


23.1Z 

T 


2  5  00 

1^ 


25.23 


CHART  XXIV. 


District  1 

Tnfluenz.a 

1918-19 
Cose  r?a+e 
c  e  r~     I  Q  Q 
be  i^^sons 
b^   occu 
b  o  +■  i  o  n 


Perc  e  nt 


■78 


3.^2 


5.57 


bei^.sons  ^m 

b^   occu-  H 

b  o  i-  i  o  n  H      ■      ■■ 


29  06 


21.0^ 


13,8  1 


i2.96 


0,00 


32  li 


District  2 

Influenza 
1918-13 

Cose  Ra+e 
per    |D0 

persons 

b^/   occu- 

batioh 

1 

1 

1 

1 

1 

1 

1 

1 

Percent 

7.81 

18.88 

22.62 

15.02 

16,^6 

12.31 

2  6,17 

O-OD 

I&.B7 

Districts 

Influenza 
1918-19 

Case  Rate 
per    too 

persons 
bj  occu- 
pati  on 


Percent 


^^.25 


21.7^ 


8.78 


per   too 

persons  M 


2^55 


5.55 


^  9-^ 


1522 


15  73 


17.^5 


U^ 


1-^ 


^1 
1^ 


CHART  XXIV.— (Con/.) 


Dis+rictI2 

Ihfluenzcj 
1918-13 

Ca-se  Rate 
per    lOU 
per^sons 
by  occu 
pa+ion 


Percent 


Districts 

Inj'luenza 
1318-19 

Case  rate 
per   100 
[oer^ons 
b^  occu- 
pation 


Percent 

DUtnct  6 

Influenza 

1918-19 

Case  ra^e 
per  100 
persons 
by  occu- 
pation 

Percent 


CHART  XXV. 


Influenza 
1920 

case  rote 
{3er   loo 

|oer5ons 

b, 

Occujoq- 

iion 

m 

7.73 

M 

8.25 

M 

8.90 

1 

9^7 

1 

9.56 

1 

10.23 

1 

1Z.59 

1 

M.2.8 

Percenl- 

7.  IZ 

11 

'J 

1 

1^ 

1 

5 

Influenza 

I92Q 
Case  Rate 

per 
lOD   male 
persons 
b^  occu- 
joation 

m 

7.78 

7.8  6 

JL 

7.98 

M 

8-55" 

1 

3.87 

I 

1 

10-78 

1 

K  81 

Percerrr 

•^  -15 

1 

It 

1 

^ 

01 
(J 

1 

1^ 

1 

S 

1^ 

^       ( 

Influenza 

1920 
Case  Rate 
per  100 
female 
[persons 
bj  occu- 
^afion 

// 

^ 

U 

^ 

1 

1 

Percent 

DOO 

DOD 

B.35 

8.24 

8.25 

9.35 

3.4^ 

10.03 

12.89 

^1 

^ 

^ 

-<:: 

^ 

1 

1^ 

^'l^ 
|xi 

^^^) 
^"1^ 

0 

1 

^ 

S 

CHART  : 

x:xvi. 

1918 

Incidence 

of 

Influenza 

■ 

in    the 
V"a  nous 

■ 

■ 

■ 

I 

1 

1 

1 

Di^tnct^ 

I 

1 

1 

1 

1 

I 

3urveyQd 

1 

1 

1 

1 

1 

1 

Perce  nf 

16.90 

17.35 

18.00 

18.30 

22.50 

25.69 

13.71 

District 

2 

1 

6 

3 

4 

5 

All 

1920 
I  ncidence 

of 
Influenza 

in   the 
various 
D  istnct^ 
surveyed 

1 

1 

1 

1 

1 

1 

Percent 

5.30 

8.H 

3.90 

iQ.4Q 

12.00 

1360 

9.55 

D  ist  rict 

z 

d 

3 

1 

5 

-^ 

All 
Districts 

Indivjcj- 

udls 

havinq 

In-fluenza 

in    both 

Epidemics 

Percent 

0.70 

r.78 

2.35 

2.90 

3  69 

3.70 

z.^o 

IJls+rlct 

2 

5 

3 

1 

5 

4 

All 
Districts 

AN    EPIDEMIOLOGIC    STUDY  155 

extremes  of  the  two  charts  we  see  some  tendency  to  an  inversion  of  the 
order.  In  1918-19  those  occupied  in  "retail  sales"  outdoors  showed 
a  low  incidence,  while  in  1920  they  were  the  highest.  So  also,  the 
incidence  in  the  school  group  changed  from  highest  in  1918  to  lowest 
in  1920.  The  incidence  in  infants  increased;  that  in  the  office  workers 
decreased.     No  general  conclusions  are  warranted  from  these  results. 

In  comparing  the  sex  incidence  by  age  groups  we  have  found  that 
females  as  a  rule  showed  a  slightly  greater  incidence  than  males. 
That  this  is  not  due  fundamentally  to  occupational  differences  is 
suggested  by  a  comparison  of  the  sex  incidence  in  the  two  epidemics 
studied.  In  1918  the  distribution  is  practically  the  same  in  the  two 
sexes  in  all  occupations  except  "Home,"  "Manual  Outdoors," 
" Retail  Sales  Indoors, "  "Retail  Sales  Outdoors "  (Chart  XXVI) .  In 
the  first  the  number  of  males  is  so  small  and  in  the  second  and  fourth  the 
number  of  females  is  so  small  that  these  cannot  justly  be  compared. 
The  group,  "Retail  Sales,"  consists  in  1918-19  of  69  males  and  27 
females,  out  of  a  total  distribution  in  the  population  of  426  males  and 
107  females.  This  is  the  only  occupation  that  showed  a  definite 
higher  incidence  among  the  females,  and  even  here  the  number  is  too 
small  for  accuracy.     In  1920  this  difference  has  practically  disappeared. 

Effect  of  race  stock. — Leichtenstern  remarks  in  his  monograph  that 
the  reported  differences  in  influenza  morbidity  among  different  races, 
such  for  instance  as  European  and  other  nationalities,  doubtless  are 
due  to  factors  other  than  genetic  racial  differences,  such  as  different 
modes  of  living,  commerce,  etc.  The  work  of  the  last  two  years  calls 
for  a  reconsideration  of  this  idea. 

Frost  in  his  valuable  work  found  that  "in  the  seven  localities  with 
considerable  colored  population  the  incidence  rates  among  the  colored 
were  uniformly  lower  than  among  the  whites,  the  difference  persisting 
after  adjustment  of  the  rate  to  a  uniform  basis  of  sex  and  age  distribu- 
tion. The  extent  of  the  difference  varied,  being  relatively  great  in 
Baltimore,  Augusta  and  Louisville,  and  very  small  in  Little  Rock. 
This  relatively  low  incidence  in  the  colored  race  is  quite  contrary  to 
what  would  have  been  expected  a  priori,  in  view  of  the  fact  that  the 
death  rate  from  pneumonia  and  influenza  is  normally  higher  in  the 
colored  than  in  the  white,  and  that  the  colored  population  lived  gener- 
ally under  conditions  presumably  more  favorable  to  the  spread  of 
contact  infection." 

Brewer,  in  his  study  of  influenza  in  September,  1918,  at  Camp 
Humphreys,  finds  that  the  colored  troops  showed  a  decidedly  lower 
rate  than  the  white  troops  throughout  the  epidemic.     He  finds  that 


156  INFLUENZA 

the  incidence  among  colored  troops  was  only  43  per  cent,  of  that 
among  whites.  The  difference  between  colored  and  white  organiza- 
tions was  probably  not  due  to  difference  in  housing.  Most  of  the 
colored  troops  were  in  tents  and  the  white  troops  were  all  in  barracks. 
But  the  42d  Company  composed  of  negroes  was  housed  in  barracks 
under  the  same  conditions  as  the  white  troops  of  other  organizations 
and  they  had  next  to  the  lowest  incidence  of  all  organizations.  Brewer 
concludes  that  the  colored  race  when  Uving  under  good  hygienic 
conditions  is  not  as  susceptible  to  influenza  as  the  white  race  under  the 
same  conditions.     The  age  distribution  was  the  same  in  both  groups. 

Armstrong  concluded  from  figures  based  on  reported  cases  of 
influenza  that  in  the  autumn  of  1918  proportionately  four  times  as 
much  influenza  and  pneumonia  was  reported  among  the  Itahans  as  was 
reported  for  the  rest  of  the  Framingham  community,  made  up  largely 
of  Irish  or  Irish- American  stock.  On  the  contrary,  an  examination  of  a 
large  proportion  of  the  population  of  that  town  showed  a  tuberculosis 
incidence  among  the  Italian  race  stock  of  .48,  in  contrast  to  an  inci- 
dence among  the  Irish  of  4.85  per  cent,  and  of  2.16  per  cent,  in  the 
entire  population.  Armstrong  contrasts  the  relative  insusceptibility 
of  Itahan  stock  to  tuberculosis,  with  the  apparent  marked  suscepti- 
bility to  acute  disease  of  the  respiratory  tract,  such  as  influenza 
and  pneumonia;  and  the  high  susceptibility  of  the  Irish  to  tuberculosis, 
with  their  low  susceptibihty  to  acute  respiratory  infection. 

With  regard  to  our  work  it  is  sufficient  to  state  that  the  lowest 
incidence  in  both  epidemics,  as  well  as  in  recurrent  cases,  was  in  the 
Irish  tenement  districts.  Both  the  Jewish  and  the  ItaHan  tenement 
districts  were  slightly  higher  in  both  epidemics  (Charts  XIX  and  XXI) . 
The  age  distribution  of  the  entire  population  of  each  of  these  three 
districts  was  about  the  same,  so  it  does  not  appear  that  the  slightly 
lower  incidence  among  the  Irish  is  due  to  a  variation  in  the  age  dis- 
tribution of  the  population. 

The  subject  of  race  in  relation  to  influenza  will  be  discussed  further 
under  mortality. 

Mortality. 

According  to  Marchese,  in  1387  at  ForU  in  Italy,  not  a  person 
escaped  the  disease,  but  only  a  few  died.  Gassar  says  that  during  the 
same  epidemic  in  Germany  the  patients  suffered  four,  or  at  most  five, 
days  with  the  most  disagreeable  catarrhal  symptoms  and  delirium,  but 
recovered,  and  only  very  few  were  removed  by  death. 

Pasquier  remarks  concerning  an  epidemic  in  1411  that  an  infinitude 
of  individuals  were  attacked  but  that  none  died. 


AX    EPIDKMIOLOGir    STUDY  157 

Concorninj?  the  opidemic  of  1414  in  France,  Lobinoau  rolatos  that 
the  disease  was  fatal  only  for  the  aged.  Mezeray  also  speaks  of  the 
high  mortality  of  the  old  in  this  epidemic. 

Regarding  the  pandemic  of  lolO,  Thomas  Short  remarks  that  none 
died  except  some  children.  Mezeray,  on  the  other  hand,  says  that  the 
disease  had  claimed  many  victims. 

Pasquier  and  Valleriola  both  write  of  the  epidemic  of  lo57,  in 
France,  as  being  distinctly  mild  in  character.  Children  only  who 
could  not  freely  cough  out  the  phlegm  died.  Coyttar  speaks  of  the 
absence  of  death  except  in  tuberculous  patients. 

In  the  pandemic  of  1580  individual  observers  report  enormous 
death  rates.  Thus,  according  to  Schenkius,  the  disease  killed  9,000 
persons  in  Rome,  while  ]\Iadrid,  Barcelona  and  other  Spanish  cities 
were  said  to  have  been  nearly  depopulated  by  the  disease.  This  high 
mortality  was,  however,  even  at  that  time  attributed  by  some  physi- 
cians to  the  injudicious  employment  of  venesection.  Throughout 
the  more  recent  history  of  pandemic  influenza  opinion  seems  to  have 
been  nearly  unanimous  that  blood  letting  has  had  very  bad  results  in 
the  outcome  of  influenza  cases.  Remarks  to  this  effect  have  been  made 
by  the  contempories  of  nearly  everj'  epidemic  since  1580. 

According  to  Rayger  and  others  during  the  epidemic  of  1675, 
nobody  died  of  the  disease  itself  with  the  exception  of  debilitated 
persons,  although  it  spared  neither  the  w'eak  nor  the  strong. 

Concerning  the  epidemic  of  1688,  Thomas  Short  writes  for  England 
that  though  not  one  of  fifteen  escaped  it,  yet  not  one  of  a  thousand 
that  had  it  died. 

In  1712,  Slevogt  writes  that  in  Germany  "Fear  soon  vanished  when 
it  was  seen  that  although  it  had  spread  all  over  the  city,  it  left  the 
sick  with  equal  rapidity." 

Finkler  remarks,  concerning  1729-30,  that,  "The  great  mortality 
which  attended  the  epidemic  in  England  and  Italy  seems  somewhat 
remarkable.  Thus  Hahn  states  that  in  London  in  the  month  of  Septem- 
ber one  thousand  persons  died  each  week,  and  in  Mayence  forty  persons 
daily.  Most  likely,  however,  other  diseases  which  were  present  at  the 
same  time  added  their  quota  to  the  mortality,  especially  as  the  disease 
in  other  places,  for  example  in  Germany,  ran  a  benign  course." 

Perkins,  Huxham,  Pelargus,  Carl  and  others,  concerning  the 
epidemic  of  1732-33,  all  testify  that  the  disease  was  of  very  low  fatahty. 

In  1742  the  epidemic  was  evidenced  by  an  enormous  morbidity  but 
the  disease  was  not  dangerous  as  a  general  rule  although  Huxham 
occasionally  speaks  of  the  virulent  character  of  the  disease  in  England, 


158  INFLUENZA 

and  Cohansen  says  that  in  January,  1743,  over  8,000  persons  died 
from  influenza  in  Rome  and  5,000  in  Mayence. 

We  have  the  testimony  of  Robert  Whytt,  for  1758,  and  that  of 
Razoux  and  Saillant  and  Ehrman  for  1762,  as  to  the  low  mortahty  of 
the  epidemic  for  those  years. 

According  to  Heberden  the  same  was  true  for  1775,  while  Webster 
tells  us  for  1780  that  the  disease  was  not  dangerous  but  its  effects  were 
seen  the  following  year  in  the  increased  number  of  cases  of  phthisis. 

Finkler  remarks  concerning  the  epidemic  of  1802,  "The  mortality  in 
this  epidemic  was  small,  only  the  abuse  of  venesection  brought  many  to 
the  grave.  Thus,  so  many  farmers  are  said  to  have  died  in  Russia 
from  it  that  venesection  was  forbidden  by  an  imperial  ukase.  Jonas 
says  that  many  patients  were  bled  either  on  the  advice  of  a  simple 
village  barber  or  by  their  own  wish,  and  most  of  them  died.  In 
Prussia  also  bleeding  was  declared  detrimental  by  the  Government." 

He  continues  regarding  1836-37,  that,  "In  London  there  died, 
during  the  week  ending  January  24,  1837,  a  total  of  871  persons,  and 
among  these  deaths  there  were  295  from  disease  of  the  respiratory 
organs;  during  the  week  ending  January  31st,  out  of  a  total  of  860 
deaths  there  were  309  from  diseases  of  the  respiratory  organs." 

Watson,  in  describing  the  epidemic  of  1847, 'discusses  the  mortahty: 

"The  absolute  mortality  has  been  enormous;  yet  the  relative  mor- 
tality has  been  small.  You  will  hear  people  comparing  the  ravages  of 
the  influenza  with  those  of  the  cholera,  and  inferring  that  the  latter  is 
the  less  dangerous  complaint  of  the  two;  but  this  is  plainly  a  great 
misapprehension.  Less  dangerous  to  the  community  at  large  (in  this 
country  at  least)  it  certainly  has  been;  but  infinitely  more  dangerous  to 
the  individuals  attacked  by  it.  More  persons  have  died  of  the  influ- 
enza in  the  present  year  than  died  of  the  cholera  when  it  raged  in  1832; 
but  then  a  vastly  greater  number  have  been  affected  with  the  one 
disease  than  with  the  other.  I  suppose  that  nearly  one-half  of  those 
who  were  seized  with  the  cholera  perished;  while  but  a  very  small 
fraction,  indeed,  not  more  probably  than  two  per  cent,  of  those  who 
suffered  influenza  have  sunk  under  it." 

Leichtenstern  remarks  on  the  very  low  mortality  of  1889-90.  In 
Munich  0.6  per  cent,  died;  in  Rostock  0.8  per  cent.;  in  Leipzig  0.5  per 
cent.;  in  fifteen  Swiss  cities  0.1  per  cent. ;  in  Karlsruhe  0.075  per  cent.; 
in  Mecklenburg-Schwerin  1.2  per  cent.  This  does  not,  however, 
include  the  numerous  deaths  from  complications,  as  from  pneumonia, 
and  does  not  express  the  true  mortality. 

Newsholme  gives  the  following  table  for  mortahty  from  influenza, 


AN    EPIDEMIOLOGIC    STUDY 


159 


bronchitis  and  pneumonia,  in  England  and  Wales  during  the  epidemic 
years  and  the  years  immediately  preceding  them.  The  figures  express 
annual  death  rate  per  million  of  population.  The  highest  rate  was 
reached  in  1891.  The  table  does  not  include  deaths  registered  as  from 
other  diseases,  but  due  directly  or  indirectly  to  influenza.  Respirator^' 
diseases  in  general  show  a  greatly  increased  death  rate  in  years  in 
which  influenza  is  epidemic.  Such  is  also  true  to  some  extent  with 
diseases  of  the  nervous  and  the  circulatory  systems. 


Death  rate  per  million 

Non-epidemic  years. 

Epidemic  years. 

of  population  from 

1887       1       1888 

1889 

1890       1       1891       ' 

1892 

Influenza 

3 
2,117 
1,113 

3 
2,041 
1,093 

2 
1,957 
1,022 

157            574 
2,333     1    2,593 
1,404     1    1,471     1 

533 

Bronchitis 

Pneumonia 

2,266 
1,250 

In  a  report  by  the  United  States  PubUc  Health  Service  early  in 
1919  the  death  rates  from  all  causes  in  twelve  large  cities  of  this  country 
were  compared  for  1889-90  and  for  1918-19.  It  was  found  that  while 
considerable  irregularity  in  the  curves  was  evident,  the  curves  of  the 
two  epidemics  manifested  on  the  whole  quite  a  striking  similarity  for 
the  same  cities  considered  individually  and  for  the  group  as  a  whole. 
The  death  rate  rose  to  a  much  higher  point  during  the  autumn  wave 
of  the  1918  epidemic  than  in  the  epidemic  of  1889-90  in  nine  out  of  the 
twelve  cities.  During  both  epidemics  the  rate  was  rel'^tively  low  in 
St.  Louis,  Milwaukee  and  Minneapolis.  The  mortality  in  all  of  these 
cities  was  26.7  in  1889,  as  against  35.2  for  1918.  In  the  peak  week  the 
rate  rose  to  55.6  in  1918  as  against  35.4  in  1889. 

The  influenza  deaths  in  Massachusetts  in  the  year  1890  during  a 
period  of  fifty  days  were  estimated  by  Abbott  to  have  been  2,500.  In 
1918  Jordan  estimates  the  mortality  for  the  same  state  to  have  been 
six  times  as  great.  The  population  of  the  state  had  not  doubled  in 
the  interval.  The  highest  mortality  from  influenza  in  Massachusetts 
during  the  1889-93  epidemic  occurred  in  January,  1892,  during  which 
month  the  total  deaths  amounted  to  6,309  which  was  greater  by  2,246 
than  the  mean  monthly  mortality  of  the  year,  and  greater  by  more 
than  1,000  than  the  mortality  of  any  month  in  the  ten  year  period 
1883-92. 

A  comprehensive  comparison  of  the  damage  done  by  influenza  in 
1918  with  the  deaths  from  other  plagues  has  been  made  by  Vaughan 
and  Palmer. 


160  INFLUENZA 

"The  pandemic  of  1918,  when  compared  with  that  of  1889-90  is 
estimated  to  have  caused  six  times  as  many  deaths. 

"During  the  four  autumn  months  of  1918,  338,343  cases  of  influ- 
enza were  reported  to  the  Surgeon  Generah  This  means  that  in  the 
camps  of  this  country  one  out  of  every  four  men  had  influenza. 

"The  combination  between  influenza  and  pneumonia  during  the 
fall  of  1918  seems  to  have  been  closer  and  more  destructive  than  in  any 
previous  pandemic.  During  the  autumn  season  there  were  reported 
to  the  Surgeon  General  61,691  cases  of  pneumonia.  This  means  that 
one  out  of  every  twenty-four  men  encamped  in  this  country  had  pneumonia. 

"During  the  same  period  22,186  men  were  reported  to  have  died 
from  the  combined  effects  of  influenza  and  pneumonia.  This  means 
that  among  the  troops  in  this  country  one  out  of  every  sixty-seven  died. 

"This  fatahty  has  been  unparallelled  in  recent  times.  The  influ- 
enza epidemic  of  1918  ranks  well  up  with  the  epidemics  famous  in 
history.  Epidemiologists  have  regarded  the  dissemination  of  cholera 
from  the  Broad  Street  Well  in  London  as  a  catastrophe.  The  typhoid 
epidemic  of  Plymouth,  Pa.,  of  1885,  is  another  illustration  of  the  dam- 
age that  can  be  done  by  epidemic  disease  once  let  loose.  Yet  the 
accompanying  table  shows  that  the  fatality  from  influenza  and  pneu- 
monia at  Camp  Sherman  was  greater  than  either  of  these.  Compared 
with  epidemics  for  which  we  have  fairly  accurate  statistics  the  death 
rate  at  Camp  Sherman  in  the  fall  of  1918  is  surpassed  only  by  that  of 
plague  in  London  in  1665  and  that  of  yellow  fever  in  Philadelphia  in 
1793. 

"The  plague  killed  14  per  cent,  of  London's  population  in  seven 
months'  time.  Yellow  fever  destroyed  10  per  cent,  of  the  population 
of  Philadelphia  in  four  months.  In  seven  weeks  influenza  and  pneu- 
monia killed  3.1  per  cent,  of  the  strength  at  Camp  Sherman.  If  we 
consider  the  time  factor,  these  three  instances  are  not  unhke  in  their 
lethality.  The  plague  killed  2  per  cent,  of  the  population  in  a  month, 
yellow  fever  2.5  per  cent,  and  influenza  and  pneumonia  1.9  per  cent. 

"In  four  months  typhoid  fever  killed  1.5  per  cent,  of  the  soldiers 
encamped  in  this  country  during  the  war  with  Spain.  Influenza  and 
pneumonia  killed  1.4  per  cent,  of  the  soldiers  in  our  camps  in  1918  and 
it  also  covered  a  period  of  four  months." 

The  Bureau  of  the  Census  has  made  the  following  report  concern- 
ing influenza  deaths  in  the  United  States : 

"In  forty-six  American  cities,  having  a  combined  population  of 
only  a  Kttle  more  than  one-fifth  the  total  for  the  country,  the  mor- 
tality resulting  from  the  influenza  epidemic  during  the   nine  weeks 


AN    EPIDEMIOLOGIC    STIDY  101 

period  ciulocl  Xovcnil)or  0th  was  nearly  (l()iil)lc  that  in  the  A.  E.  F. 
from  the  time  the  first  contingent  landed  in  France  until  the  cessation 
of  hostilities." 

The  mortality,  even  as  the  morbidity,  has  varied  in  different 
localities  and  at  different  periods.  The  low  morbidity  and  mortality 
in  the  spring  of  1918  has  been  frequently  mentioned.  Among  the 
Esquimaux  in  Alaska  the  death  toll  was  terrific.  Whole  villages  of 
Esquimaux  lost  their  entire  adult  population.  It  has  been  estimated 
that  in  British  India  the  death  roll  totalled  5,000,000.  "The  central, 
northern  and  western  portions  of  India  w^ere  the  worst  sufferers.  The 
hospitals  in  the  Punjab  were  choked  so  that  it  was  impossible  to  move 
the  dead  quickly  enough  to  make  room  for  the  dying.  The  streets 
and  lanes  of  the  cities  were  littered  with  dead  and  dj'ing  people.  The 
postal  and  telegraph  services  were  completely  disorganized;  the  train 
service  continued,  but  at  all  principal  stations  dead  and  dying  people 
were  being  removed  from  the  trains.  The  burning  ghats  and  burial 
grounds  were  literally  swamped  with  corpses,  while  an  even  greater 
number  awaited  removal.  The  depleted  medical  service,  itself  sorely 
stricken  by  the  epidemic,  w^as  incapable  of  dealing  with  more  than  a 
minute  fraction  of  the  sickness  requiring  attention.  Nearly  every 
household  w^as  lamenting  death,  and  everywhere  terror  and  confusion 
reigned.     Xo  part  of  the  Punjab  escaped." 

The  Bureau  of  the  Census  estimates  that  445,000  deaths  from  the 
epidemic  of  influenza  occurred  in  the  United  States  in  the  period  be- 
tween September  1st  and  December  31st,  1918.  There  is  no  doubt  but 
that  the  total  death  toll  for  that  epidemic  exceeded  500,000  individuals. 

According  to  Winslow  and  Rogers,  the  two  highest  annual  death 
rates  on  record  in  Connecticut  are  both  rates  of  19.4  per  1,000  and 
these  tw^o  rates  are  for  the  influenza  epidemic  years  of  1892  and  1918. 
In  the  earlier  of  these  tw^o  the  normal  general  death  rate  was  several 
points  higher  than  it  is  today,  so  that  the  effect  of  the  recent  epidemic 
was  much  more  serious  than  was  that  of  its  predecessor.  For  a 
single  month  the  death  toll  of  October,  1918,  was  absolutely  unprece- 
dented in  Connecticut.  They  estimate  that  the  epidemic  between 
September,  1918,  and  January,  1919,  cost  the  State  5.5  lives  per  1,000 
population,  or,  in  all,  7,700  lives. 

In  the  United  States  Army  there  was  a  total  of  688,869  admissions 
for  influenza.  The  total  deaths  ascribed  to  the  disease  are  39,731, 
which  gives  a  rate  of  15.64  per  1,000  for  the  acute  respiratory  diseases 
out  of  the  total  disease  death  rate  of  18.81  for  the  year.  In  1915  the 
per  cent,  of  deaths  from  this  group  of  infections  was  under  18  per  cent. 


162  INFLUENZA 

of  the  total  from  all  diseases.  During  the  last  four  months  of  1918, 
11,670  deaths  from  influenza  and  pneumonia  occurred  in  the  American 
Expeditionary  Forces  in  France.  There  were  approximately  1,600,000 
officers  and  men  in  the  United  States  and  an  equal  number  in  France. 
Carnwath  gives  the  following  comparison  of  the  number  of  deaths 
in  London  and  in  certain  American  cities  from  influenza  and  all  forms 
of  pneumonia  during  the  eight  weeks  of  the  1918-19  epidemic. 

Deaths  in  London  and  in  American  cities. 

Rate  eight  weeks 
Number  of  per  100,000  of 

deaths.  population. 

London 13,744  341 

New  York... 20,681  360 

Chicago..... 8,785  343 

Philadelphia 12,806  749 

Boston 4,211  548 

The  cause  of  death  in  the  vast  majority  of  cases  is  some  form  of 
pneumonia.  In  fact  it  has  been  questioned  whether  influenza  uncom- 
plicated can  cause  a  fatal  issue.  Post-influenzal  meningitis  has  been 
the  cause  of  death  in  an  appreciable  number  of  cases.  More  remotely 
the  disease  has  caused  many  deaths  by  hastening  the  fatal  outcome  of 
what  were  otherwise  subacute  or  chronic  conditions  of  the  respiratory, 
cardiovascular,  or  renal  systems. 

Vaughan  and  Palmer  record  that,  "The  pandemic  of  influenza  in 
1918  seems  to  have  been  more  closely  associated  with  the  pneumonias 
than  appears  in  any  previous  pandemic.  From  the  reports  as  sent  to 
the  Surgeon  General's  Office,  it  appears  that  uncomplicated  influenza 
was  not  by  any  means  a  fatal  disease  and  that  the  high  death  rate  was 
due  to  the  pneumonias  which  followed.  Pneumonia  is  a  serious  disease 
at  all  times.  Recent  records  for  the  United  States  Army  show  that  the 
case  mortality  rate  for  this  disease  has  been  as  follows  during  the 
different  periods  of  the  last  two  years : 

Per  cent. 

The  year  1917 11.2 

6  winter  months,  1917-18 23. 1 

5  summer  months,  1918 18.8 

4  autumn  months,  1918  (Influenza  period) 34.4 

"It  is  not  strange  that  once  pneumonia  has  secured  a  foothold  in 
patients  already  weakened  by  influenza  their  chances  of  recovery  were 
lessened." 

WooUey  reports  that  for  the  troops  stationed  at  Camp  Devens,  Mass. 
there  were  no  fatalities  from  uncompHcated  influenza.     In  every  fatal 


AN    EPIDEMIOLOGIC    STUDY  163 

case  but  two  a  diagnosis  of  pneumonia  was  made,  and  in  these  two 
cases  pure  cultures  of  pncumococcus  were  obtained  from  the  blood 
after  death,  so  it  appears  that  they  were  cases  of  pneumococcus 
septicemia.  Up  to  October  29,  1918,  19  per  cent,  of  the  total  number 
of  influenza  cases  reported  developed  pneumonia  and  of  these  there 
was  a  case  mortality  of  27.9  per  cent.  The  mortality  rate  among  the 
influenza  cases  was  5.4  per  cent. 

At  Camp  Humphreys,  Virginia,  16  per  cent,  of  the  camp  was 
attacked  by  the  disease;  28  per  cent,  of  influenza  cases  had  pneumonia; 
10  per  cent,  of  influenza  cases  died;  and  35  per  cent,  of  pneumonia 
cases  died.  One  and  six  tenths  per  cent,  of  the  population  of  the 
camp  died  from  influenza.  The  camp  had  an  average  strength  of 
26,600  individuals.  Fifty-two  per  cent,  of  the  entire  number  of  cases 
occurred  during  the  peak  week  which  ended  October  4th. 

Between  September  21st  and  October  18th,  1918,  9,037  patients 
were  admitted  to  the  Base  Hospital  at  Camp  Grant.  This  represented 
about  one-fourth  of  the  strength  of  the  camp.  Of  these  26  per  cent, 
developed  pneumonia  and  43  per  cent,  of  the  pneumonia  cases  died. 
Death  occurred  to  about  11  per  cent,  of  the  total  admissions. 

The  death  rate  at  Camps  Devens,  Sherman  and  Grant  were  among 
the  highest  of  all  of  the  camps  in  this  country.  The  annual  death 
rate  from  all  causes  per  1,000  for  the  four  last  months  of  1918  were  132 
for  Camp  Cody,  123  for  Syracuse,  116  for  Camp  Sherman,  102  for 
Camp  Beauregard,  97.3  for  Camp  Grant,  75.0  for  Camp  Dix,  67.0  for 
Camp  Devens.  These  seven  camps  stood  out  high  above  the  majority. 
By  far  the  majority,  28  camps,  had  an  annual  rate  between  61.9  and 
25.5  per  1,000,  Only  four  camps  recorded  lower  rates  than  the  latter 
figure. 

The  Municipal  Statistics  of  Paris  showed  that  during  the  first 
half  of  October,  1918,  the  average  weekly  mortality  was  from  two  to 
three  times  that  of  non-epidemic  years.  The  returns  for  the  Depart- 
ments of  France  also  showed  a  mortality  three  times  above  the  average 
for  previous  years,  though  not  uniformly  so.  In  the  Departments  the 
mortaUty  from  influenza  did  not  exceed  10  per  cent,  and  in  many  cases 
it  was  below  5  per  cent.  On  the  other  hand  cases  admitted  to  hospital, 
which  consisted  of  the  worst  forms  of  the  disease,  showed  a  mortality 
varying  between  12  and  30  per  cent.  Returns  received  from  Italy 
were  similar.  The  disease  in  that  country  was  especially  severe  in  the 
northern  part  and  in  the  provinces  bordering  on  Switzerland.  Marcus, 
of  Stockholm,  reported  in  September,  1918,  that  the  epidemic  in 
Sweden  was  running  a  very  severe  course,  more  than  1,000  deaths 

14 


164  INFLUENZA 

having  occurred  up  to  the  time  of  his  report.  According  to  Weber, 
2,770  deaths  occurred  in  Berlin  during  October,  1918,  from  influenza 
and  pneumonia  alone.  In  Vienna  there  died  from  influenza  between 
September  1st  and  October  19th,  1918,  3,125  persons.  The  deaths 
in  Vienna  from  influenza  and  pneumonia  normally  total  40  to  50  per 
week.  At  the  highest  point  of  the  epidemic  this  number  had  increased 
to  1,468.  Bohm  estimates  the  total  influenza  incidence  in  Vienna  as 
180,000  cases,  with  a  probable  mortality  around  1.7  per  cent.  Dunlop 
estimates  that  the  total  number  of  influenza  deaths  in  Scotland  in 
the  winter  of  1918-19  may  be  assessed  at  20,000. 

A.  Giltay  has  compared  the  epidemics  of  1890  and  1900  with  that  of 
1918  as  regards  mortality,  in  Amsterdam.  He  has  studied  figures  for 
seven  consecutive  weeks  in  each  of  the  three  periods  under  observation 
and  found  that  the  maximum  figures  for  mortahty  were  61.5  in  1890, 
41.2  in  1900,  and  52.7  in  1918,  but  if  these  figures  are  compared  with 
the  average  mortality  for  the  year  it  is  found  that  the  increase  of 
mortality  as  the  result  of  influenza  alone  is  39.3  for  1890,  24.5  for  1900, 
and  40.3  for  1918.  Thus  the  present  epidemic  is  more  severe  than 
that  of  1890. 

Many  reported  mortality  figures  are  without  value  because  they  are 
either  death  rates  in  selected  groups  such  as  those  in  a  hospital,  or, 
because  the  report  does  not  state  the  status  of  the  individual.  Thus, 
Hoppe-Seyler  stated  at  a  meeting  of  the  Kiel  Medical  Society  that  of 
577  cases  treated  in  the  Municipal  Hospital,  nearly  all  of  which  were 
severe,  28.9  per  cent.  died.  This  was  reduced  to  18  per  cent,  after 
deducting  the  cases  admitted  in  a  moribund  condition.  Again, 
Rondopoulos  reports  that  the  October  wave  in  Greece  resulted  in  a 
mortality  of  from  15  to  24  per  cent,  in  different  localities. 

Just  as  current  vital  statistics  are  of  little  value  in  determining 
the  morbidity  rate,  so  also  they  cannot  be  relied  upon  in  obtaining 
fatality  percentages.  In  organizations  such  as  the  Army,  where  all 
cases  are  reported,  we  may  get  some  idea  of  the  fatality  rate.  The 
deaths  in  the  United  States  Army  have  already  been  discussed. 
Marcus,  of  Stockholm,  reports  that  the  military  records  showed  that 
there  had  been  34,000  cases  in  the  Swedish  Army,  with  444  deaths, 
making  a  mortality  of  1.3  per  cent,  in  that  Army. 

House  surveys  also  give  a  fair  idea  of  the  mortality.  Winslow  and 
Rogers  conclude  that  the  fatality  rate  was  as  a  rule  somewhere  between 
two  and  four  deaths  per  100  cases,  the  lower  being  more  likely  to  be 
correct.  Reeks  found  in  his  house  census  that  there  had  been  3.9 
deaths  per  100  cases  in  the  autumn  of  1918.     Carnwath  reports  that 


AN    EPIDEMIOLOGIC    STUDY  165 

Dr.  Nivon,  in  his  census,  discovered  that  out  of  1 ,108  cases  in  the  spring 
and  autumn  of  1918  there  were  but  15  deaths,  which  would  fj;ive  a 
fatality  rate  of  1.3  per  100  cases. 

Frost  has  found  from  his  large  survey  that  the  ratio  of  deaths  to 
total  cases  of  influenza  varied  in  the  localities  surveyed  from  3.1  per 
cent,  in  New  London  as  a  high  point  to  2.8  per  cent,  in  San  Antonio, 
Texas.  There  was  some  apparent  relationship  between  fatahty  rate 
and  geographic  distribution,  the  higher  rates  being  in  San  Francisco  on 
the  Pacific  Coast,  and  in  the  localities  studied  on  the  north  half  of  the 
Atlantic  Seaboard,  and  the  lower  rates  being  in  the  central  and  south- 
ern states.  The  fatality  rate  on  the  Pacific  Coast  was  2.33,  on  the 
Atlantic  Seaboard  2.05,  and  in  the  last  district  1.08  per  cent. 

Our  own  figures  correspond  very  closely  with  those  of  Frost. 
Among  the  10,000  living  individuals  surveyed  in  1920  there  were 
1,970  cases  of  influenza  in  1918.  Add  to  this  the  50  deaths  for  1918, 
which  were  not  included  in  the  10,000  living  individuals,  which  makes 
a  total  incidence  of  2,021.  This  case  fatahty  rate  of  2.47  per  100, 
corresponds  closely  to  Frost's  rate  for  the  North  Atlantic  Seaboard. 

The  relative  mildness  of  the  1920  recurrence  is  indicated  in  the 
lower  case  fatality  rate.  Fourteen  out  of  955  cases  died,  giving  a  rate 
of  1.47  per  100  cases. 

Mortality  by  sex. — There  is  not  a  uniformity  of  opinion  as  to  which 
sex  suffered  the  higher  fatality  rate  during  the  1918-19  spread. 
Winslow  and  Rogers  found  for  Connecticut  a  distinctly  heavier  mor- 
tality among  males  for  the  last  four  months  of  1918,  58  per  cent,  of  the 
influenza-pneumonia  deaths  being  among  this  sex.  They  believe  that 
this  is  probably  due  to  a  greater  exposure  to  the  origi:^al  infection. 

Frankel  and  Dublin  point  out  that  in  a  study  of  70,729  policy 
holders  of  the  Industrial  Department  of  the  Metropolitan  Life  Insur- 
ance Company  in  the  period  from  October  1,  1918,  to  June,  1919,  the 
death  rates  for  males  and  females  were  practically  the  same  for  both 
white  and  colored  individuals. 

The  excess  of  males  over  females  among  the  whites  is  only  three 
per  cent.,  and  there  was  no  excess  among  colored.  In  contrast,  the 
respiratory  diseases,  including  influenza-pneumonia,  under  normal 
conditions,  show  a  higher  mortality  incidence  among  males  than 
among  females.  In  the  seven  year  period  from  1911  to  1917  the  mor- 
tality rate  showed  an  excess  of  18  per  cent,  males  over  females,  among 
whites,  and  of  30  per  cent,  among  colored.  This  would  seem  to  indi- 
cate that  the  effect  of  the  epidemic  was  not  much,  if  any,  greater  on 
males  than  on  females,  and  suggests  that  the  excess  mortality  caused 


166  INFLUENZA 

by  the  epidemic  did  not  operate  on  the  sexes  as  the  normal  mortalitj'' 
from  influenza-pneumonia  had  in  previous  years. 

Dunlop  finds  that  in  a  study  of  10,797  deaths  registered  in  Scotland 
up  until  the  end  of  December,  1918,  52.44  per  cent,  were  females  and 
47.56  were  males.  These  were  for  deaths  reported  as  due  only  to 
influenza.  Apert  and  Fhpo  found  a  decided  predominance  among  the 
female  deaths  in  Paris.  In  both  of  these  observations  the  absence 
from  the  civihan  population  of  male  inhabitants  of  mihtary  age  ob- 
scured correct  comparative  statistics. 

Once  again.  Frost  gives  the  most  comprehensive  discussion  of  the 
subject.  He  found,  as  we  have  stated,  that  the  influenza  case  inci- 
dence in  persons  over  fifteen  years  of  age  was  higher  in  females  than 
in  males,  and  that  in  persons  under  fifteen  the  relative  incidence  as 
between  males  and  females  is  variable,  but  with  very  sUght  excess  in 
males  for  the  localities  studied,  combined.  On  the  other  hand,  the 
case  fatahty,  the  per  cent,  of  influenza  cases  dying,  under  fifteen  years 
of  age,  was  higher  in  females  than  in  males.  Over  sixty  years  of  age 
it  was  considerably  higher  among  the  females,  but  between  the  ages 
of  fifteen  and  sixty  the  general  tendency  was  to  a  much  higher  case 
fatahty  among  the  males.  The  difference  was  greatest  between  the 
ages  of  20  and  40.  The  case  fatality  between  the  ages  of  15  and  45 
in  the  group  of  southern  and  central  states  was  in  decided  contrast  to 
that  in  the  Northern  Atlantic  and  Pacific  groups,  the  case  fatality  in 
the  former  being  remarkably  low  in  both  sections  and  slightly  higher 
in  females  than  in  males.  He  suggests  that  in  the  south  and  middle 
west  where  the  epidemic  was  generally  milder  in  respect  to  mortalitj^ 
than  in  the  northeast  and  far  west,  the  essential  difference  was  not  in 
case  incidence,  but  in  case  fatahty,  especially  in  persons  from  15  to  45 
years  of  age,  and  in  the  relatively  low  case  fatahty  among  young  male 
adults.  Frost  makes  the  important  point  that  the  relative  mortahty 
is  determined  more  accurately  by  case  fatality  than  by  case  incidence, 
and  that  without  a  fuU  and  exact  knowledge  of  the  variations  in  case 
fatahty,  statistics  of  mortality  are  by  no  means  translatable  to  terms  of 
relative  morbidity.  The  fact  that  certain  cities  showed,  as  described 
by  Pearl,  relatively  high  mortahty  rates,  does  not  give  conclusive  evi- 
dence that  the  morbidity  was  higher  in  these  cities  than  elsewhere. 
The  lower  influenza  case  fatahty  in  females  from  15  to  60  years  of  age 
appears  to  be  accounted  for  in  part  at  least;  first,  by  a  decreased 
incidence  of  pneumonia  as  compared  with  the  males;  and,  second,  by  a 
lower  fatahty  in  those  cases  which  did  develop  pneumonia. 

The  relatively  small  number  of  fatahties  in  our  own  records  do  not 


AN    EPIDEMIOLOGIC   STUDY 


167 


warrant  a  classification  by  age  groups.  We  found  that  for  all  ages 
in  1018  7.9  per  cent,  of  females  developed  pneumonia  as  contrasted 
with  6.8  per  cent,  males.  This  does  not  include  those  who  died.  In 
1920,  1.87  per  cent,  of  the  male  cases  died,  while  only  0.37  per  cent, 
of  the  females  died.  Five  and  fifteen-hundredths  per  cent,  of  all  male 
cases  developed  pneumonia  and  recovered,  and  3.56  of  the  females  did 
likewise.  In  1920  a  higher  proportion  of  males  than  females  developed 
pneumonia,  and  likewise  a  higher  proportion  died. 

Relationship  of  age. — ^Leichtenstern  has  summarized  the  results  for 
the  epidemic  of  thirty  years  ago,  in  saying  that  the  death  rate  for 
children  under  one  year  was  little  disturbed  by  the  influenza  epidemic; 
that  there  was  very  little  increase  in  mortality  in  the  other  ages  of 
childhood;  that  the  higher  age  periods  showed  the  greatest  relative 
mortality  for  the  disease.  On  the  contrary,  the  records  for  England 
and  for  Switzerland  showed  during  those  periods  a  higher  death  rate 
in  children  up  to  five  years  of  age. 

Percentages. 
Ages.  1847-8  1890 

1-5 10.5  5.2 

5-20 13.1  4.3 

20-40 3.8  4.7 

40-60 18.6  36.2 

60-80 16.9  22.4 

Above  80 8.6  2.5 


Giltay  has  compared  the  age  mortality  in  Amsterdam  in  1890,  1900 
and  1918  as  shown  in  the  following  table: 


Under 
one 
year. 

1-4 

5-13 

14-19 

20-49 

50-64 

Over  64 

Total. 

1890 
1900 
1918 

8.4 

9.7 
3.0 

8.1 

8.8 

13.0 

2.3 
1.6 

8.7 

3.0 
3.2 

8.3 

30.7 
17.6 
51.9 

19.3 

18.3 

8.7 

28.1 

40.8 

6.4 

100 
100 
100 

Evans  has  studied  the  records  for  the  city  of  Chicago  in  the  epi- 
demic of  the  year  1890,  and  found  that  the  number  of  deaths  was 
highest  among  persons  from  20  to  40  years  of  age.  The  greater  in- 
crease above  the  expected  was  in  deaths  of  persons  over  60  years  of 
age.  Children  of  school  age  seemed  to  enjoy  some  relative  immunity, 
as  shown  in  the  mortality  reports. 

This  latter  age  grouping  for  30  years  ago  corresponds  with  those  of 
1918.  Frost  found  that  the  death  rate  per  1,000  was  notably  high 
in  children  under  one  year  of  age,  in  adults  from  20  to  40,  and  in 


168  ^  INFLUENZA 

persons  over  60.  The  case  fatality  from  pneumonia  in  his  series 
tended  to  be  fairly  constant,  around  30  per  cent.,  except  in  San  An- 
tonio, Texas,  where  it  was  only  18.5  per  cent.  Case  fatality  was  also 
higher  in  the  following  age  groups:  Under  one  year,  20  to  40,  and  over 
sixty. 

This  age  distribution  was  probably  the  same  in  all  countries.  Fil- 
tzos,  describing  the  epidemic  in  Greece,  said  that  the  ages  that  suffered 
most  and  had  the  most  fatal  cases  were  between  20  and  45.  In  Spain 
in  May  and  June  of  1918  the  mortality  was  much  lower  among  children 
and  the  aged  than  it  was  among  the  adults,  especially  between  20  and 
39  years  of  age.  The  disease  appeared  fatal  almost  exclusively  in 
these  ages.  In  Vienna,  29.5  per  cent,  of  all  the  fatal  cases  were 
between  the  ages  of  20  and  30.  Hoppe-Seyler  stated  that  the  ages 
of  most  of  the  cases  were  between  20  and  40  and  the  majority  between 
30  and  40,  but  that  the  mortality  was  highest  among  the  older  patients. 

Dunlop  found  that  in  Scotland  the  most  frequent  ages  at  death  were 
between  25  and  35,  25.28  per  cent,  of  the  total  being  between  these 
two  ages.  53.85  per  cent,  of  the  total  deaths  were  between  15  and 
45  years.  The  highest  age  group  death  rates  occurred  in  age  groups 
75  and  over,  and  25  to  35,  the  former  being  7.87  per  1,000,  and  the 
latter  7.12.  High  rates  also  occurred  in  age  groups  under  one,  and  65 
to  75,  the  former  being  6.49,  and  the  latter  5.33.  The  lowest  age 
group  death  rates  were  found  in  the  groups  which  included  children 
of  school  age,  5  to  15,  being  2.20  per  cent.,  and  the  age  group  10  to  15, 
being  1.80  per  cent.  Dunlop  has  apparently  only  included  those 
cases  in  which  influenza  was  diagnosed  as  the  cause  of  death,  and  has 
omitted  all  in  which  the  diagnosis  was  bronchitis  or  pneumonia. 

The  Bureau  of  the  Census  has  issued  a  report  based  on  the  mortality 
in  Indiana,  Kansas  and  Philadelphia,  for  the  period  September  1st  to 
December  31st,  1918.  It  shows  that  the  highest  rate  occurred  in  the 
age  period  from  30  to  34  years,  with  the  period  from  25  to  29  second. 
Of  all  the  deaths  tabulated  more  than  half  occurred  between  the  period 
of  20  to  40,  although  this  age  group  represents  only  33  per  cent,  of  the 
total  population  concerned. 

Age  mortality  has  been  studied  thoroughly  by  Winslow  and  Rogers 
in  Connecticut: 

"The  four  last  months  of  1917  show  a  normal  age  distribution  with 
one  quarter  of  all  deaths  occurring  under  five  years  of  age,  one  quarter 
between  5  and  40  years,  and  one-half  over  40  years,  the  proportion  of 
the  infant  deaths  decreasing  and  the  proportion  of  deaths  in  old  age 
increasing  as  one  passes  from  the  season  of  intestinal  disturbances  to 


AN    EPIDEMIOLOCJK'    STUDY  169 

the  season  of  respiratory  diseases.  In  1918  llie  distribution  of  d(!atiis 
from  all  causes  is  strikingly  different.  Instead  of  less  than  a  quarter 
of  all  deaths  occurring  between  the  ages  of  5  and  40  years,  this  period 
included  49  per  cent,  of  all  deaths  in  1918;  and  the  two  decades  between 
20  and  40  included  40  per  cent,  of  all  deaths  (as  against  only  14  per 
cent,  in  1917). 

"Considering  influenza  and  pneumonia  alone,  these  two  decades 
included  56  per  cent,  of  the  deaths,  while  only  nine  per  cent,  occurred 
at  ages  over  49.  The  decade  between  20  and  29  was  most  severely 
affected,  including  30  per  cent,  of  all  deaths,  while  the  decade  between 
30  and  39  was  a  close  second  with  26  per  cent.  An  even  higher 
incidence  occurred  at  ages  under  five  years,  as  has  been  brought  out 
in  other  investigations,  since  this  age  period  contributed  16  per  cent, 
of  all  the  influenza-pneumonia  deaths.  The  proportion  of  deaths 
from  all  causes  in  infancy  did  not  rise  even  to  normal,  but  with  the 
enormous  rise  in  total  deaths  the  maintenance  of  a  nearly  normal 
ratio,  of  course,  means  a  heavy  influenza  mortality." 

Jordan  observes  in  his  analysis  a  low  pneumonia  incidence  among 
the  pupils  of  elementary  and  high  schools.  There  were  no  deaths  in 
188  cases. 

WoUstein  and  Goldbloom  report  that  in  a  series  of  36  children  with 
influenza  and  bronchopneumonia  at  the  Babies  Hospital  in  the  City 
of  New  York,  66.6  per  cent.  died.  Achard  and  his  co-workers  review  a 
similar  series  of  32  infants  in  Paris  with  influenza.  Eight  of  the  32 
died.  In  both  of  these  studies  we  are  dealing  with  selected  groups  of 
hospital  cases  and  the  mortality  rates  are  of  little  value  for  this  type 
of  study. 

Frankel  and  Dublin  in  a  study  of  70,729  deaths  from  influenza- 
pneumonia  among  the  policyholders  of  the  Industrial  Department  of 
the  Metropolitan  Life  Insurance  Company,  find  that  during  the  normal 
period  between  1911  and  1917,  influenza-pneumonia  attacked  pri- 
marily the  first  age  period  of  life,  ages  one  to  four  years,  and  the  period 
of  late  middle  life  and  old  age.  The  rates  are  normally  minimal  be- 
tween 5  and  30  years.  In  the  last  quarter  of  1918,  on  the  other  hand, 
the  highest  rate  among  the  whites  is  in  the  period  of  early  adult  life, 
between  the  ages  of  25  and  34.  There  appear  three  modal  points 
instead  of  the  two  at  the  extremes.  They  find  that  the  excess  over 
normal  was  most  marked  in  infancy  and  early  childhood,  and  particu- 
larly in  early  adult  life,  culminating  between  the  ages  of  25  and  34. 
The  period  of  old  age  shows  no  significant  excess  during  the  period  of 
the  epidemic. 


170  INFLUENZA 

If  the  deaths  among  the  white  males  of  the  age  period  of  active 
adult  life  had  continued  throughout  the  whole  year  as  they  did  during 
the  last  quarter  of  1918,  approximately  four  per  cent,  of  the  population 
of  that  age  would  have  died. 

Frankel  and  Dublin  are  of  the  opinion  that  this  change  in  the  age 
incidence  of  influenza  mortality  between  epidemic  and  endemic  periods 
suggests  strongly  that  the  two  diseases  are  different;  that  endemic 
influenza  is  not  the  same  disease  as  epidemic  influenza.  Or  perhaps 
they  should  say  more  correctly  that  the  diseases  occurring  in  interepi- 
demic  times  which  are  reported  to  them  as  deaths  due  to  influenza- 
pneumonia  are  not  the  same  as  the  epidemic  influenza.  They  draw 
similar  conclusions  from  the  different  manner  in  which  the  white  and 
black  races  are  affected  during  the  interepidemic  and  epidemic  periods, 
from  so-called  influenza-pneumonia.  We  have  seen  from  Frost's 
results  that  it  is  hazardous  to  compare  mortality  rates  of  different 
localities  and  different  times  with  the  idea  of  comparing  the  disease, 
influenza,  itself. 

The  ages  showing  highest  mortality  in  the  autumn  of  1918  appear 
to  have  been  essentially  the  same  as  those  which  predominated  thirty 
years  ago.  There  appears  to  be  nothing  in  the  age  distribution  that 
could  be  explained  by  an  immunity  persisting  over  from  the  epidemic 
of  1889-93.  The  age  group  30  to  40  has  almost  universally  a  higher 
mortality  than  the  groups  below  20,  which  would  by  this  theory  be 
non-immune  and  would  be  expected  to  have  a  higher  rate.  The  drop 
in  rate  is  nearer  the  age  group  of  40  than  30.  The  presence  of  smaller 
or  larger  influenza  epidemics  in  the  course  of  the  thirty  years  would 
further  complicate  such  an  hypothesis. 

Relationship)  to  occupation. — Dublin  found  in  a  study  of  4, 700  miners 
that  the  death  rate  was  unusually  high  from  influenza  in  these  individ- 
uals for  the  last  quarter  of  1918.  In  fact  in  the  age  period  45  to  65  the 
rate  among  bituminous  coal  miners  is  close  to  four  times  as  high  as 
among  all  occupied  males.  The  annual  death  rate  per  thousand  for 
all  ages  among  the  former  is  50.1;  among  all  industrial  white  males, 
22.3.  The  increase  is  apparent  in  all  age  groups  from  15  to  65  in- 
clusive. These  results  are  based  on  the  records  of  the  Metropolitan 
Life  Insurance  Company. 

Density  of  population.  Rural  and  urban  environment. — There  have 
been  few  reports  which  have  like  the  above  described  clearly  variations 
due  apparently  only  to  occupational  differences.  Some  attention 
has  been  paid  to  a  comparison  of  the  rural  incidence  with  that  in  large 
cities.     Although  other  factors  play  a  part  here,  we  may  consider 


AN    EPIDEMIOLOGIC    STUDY  171 

this  under  the  general  subject  of  occupation.  Statistics  for  the  fall 
of  1918  from  the  Netherlands  show  that  with  the  exception  of  men 
over  80  years  of  age  the  mortality  was  remarkably  increased  for  both 
sexes  in  communities  of  less  than  20,000  inhabitants. 

Winslow  and  Rogers  have  studied  the  variations  in  the  urban  and 
rural  incidence  and  find  that  in  Connecticut  with  the  single  exception 
of  Tolland  County,  in  which  the  small  towns  were  severely  hit,  the 
rates  were  in  every  case  higher  in  the  large  communities.  In  New 
Haven  County,  for  instance,  among  nine  towns  which  were  purely 
agricultural,  the  combined  death  rate  from  influenza  and  pneumonia 
for  the  three  months  of  September  to  November,  inclusive,  was  9.2 
on  an  annual  basis.  For  six  towns  in  the  same  county  in  which  there 
were  manufacturing  plants  the  corresponding  rate  was  15.6.  In 
Litchfield  County  the  twelve  purely  agricultural  towns  had  a  combined 
rate  of  6.5,  whereas  among  eleven  partly  manufacturing  towns  the  rate 
was  18.3.  This  was  true  for  other  counties.  The  figures  quoted 
are  for  influenza-pneumonia  rates  only  up  to  December  1st,  but  study 
of  the  records  during  the  early  months  of  1919  did  not  show  any  change 
in  the  figures.  The  rates  for  the  entire  state  for  January,  1919,  was 
19.8,  and  that  for  the  towns  under  5,000,  only  17.5. 

These  observations  differ  somewhat  from  those  reported  by  Pearl, 
who  studied  39  large  cities  of  the  United  States  in  an  attempt  to  find  a 
correlation  between  the  explosiveness  of  the  influenza  outbreak  and  the 
density  of  population.  He  concluded  that  there  was  no  such  correla- 
tion. Pearl,  however,  was  dealing  with  cities  which  were  all  suffi- 
ciently large  to  offer  practically  complete  opportunities  for  contact 
infection,  and  the  two  reports,  therefore,  cannot  be  justly  compared. 
Winslow  and  Rogers  suggest  as  possible  causes  for  lessened  incidence 
in  rural  communities  either  diminished  opportunities  for  contact  in- 
fection or  differences  in  age  distribution  and  racial  composition  of 
the  different  populations. 

Let  us  consider  in  greater  detail  the  fate  of  both  rural  and  urban 
individuals  who  had  been  recently  drafted  into  the  military  forces  of 
this  country.  Almost  universally  the  raw  recruit  was  found  more 
susceptible  to  disease  than  was  the  seasoned  soldier.  A  report  by 
Lieutenant  W.  D.  Wallis  from  Camp  Lee  "shows  that  while  those  who 
had  been  in  the  service  less  than  one  month  constituted  only  9.19 
per  cent,  of  the  total  strength,  the}"  furnished  30.11  per  cent,  of  the 
total  deaths  from  influenza  and  consequent  pneumonia.  Further- 
more, it  is  shown  that  while  those  who  had  been  in  the  service  from 
one  to  three  months  constituted  45.18  per  cent,  of  the  camp,  they 


172  INFLUENZA 

furnished  46.24  per  cent,  of  deaths.  On  the  other  hand,  those  who 
had  been  in  the  service  more  than  three  months  constituted  46.63 
per  cent,  of  the  population  and  furnished  only  23.69  per  cent,  of  deaths. 

Lieutenant  Wallis  says:  "These  figures  show  a  much  greater  per- 
centage of  deaths  for  the  first  month  in  camp  than  the  corresponding 
proportion  of  the  population  would  warrant;  while  in  the  period  of 
three  months  or  more  of  service  the  percentage  is  less  than  half  of  that 
of  the  camp  population  having  this  length  of  service.  The  only 
approach  to  a  correspondence  is  in  the  period  from  one  to  three 
months  where  the  respective  percentages  differ  but  little  The  in- 
crease in  length  of  service  is  accompanied  by  a  progressive  decrease 
in  the  percentage  of  deaths  from  30.11  per  cent,  to  27.41  per  cent, 
to  18.87  per  cent.,  although  only  9.19  per  cent,  of  the  population  in 
the  camp  falls  within  the  class  of  less  than  one  month's  service. 

''The  incidence  of  mortality  is  in  the  first  month's  service  more 
than  three-fold  the  percentage  of  the  number  of  men;  and  in  the  period 
of  three  months  or  more  of  service  is  scarcely  more  than  half  of  the 
percentage  of  the  number  of  men  of  the  camp  in  that  group. 

"The  fact  that  the  case  mortality  is  higher  among  those  who  came 
from  rural  homes  than  among  those  who  came  from  cities  seems  to  hold 
even  after  three  month's  of  service,  or  more." 

Vaughan  and  Palmer  found  that  the  case  fatality  at  Camp  Dix 
among  those  who  came  from  cities  with  a  population  of  10,000  or  more 
was  10.8;  while  among  those  who  came  from  more  rural  homes  the 
rate  was  15.8,  although  the  average  service  of  both  groups  was  the 
same. 

The  Camp  Surgeon  of  Camp  Grant  concluded  from  his  records 
that  the  new  recruit  is  more  susceptible  to  influenza  and  is  more  apt 
to  succumb  than  is  the  man  who  has  been  trained  and  is  accustomed 
to  Army  life. 

Wooley  reports  data  collected  from  four  Infantry  organizations  at 
Camp  Devens  comprising  15,502  men.  Of  9,559  men  who  had  been 
in  camp  less  than  five  months,  3,575  or  37.5  per  cent,  developed 
influenza,  whereas  of  5,943  men  who  had  seen  more  than  five  months 
service  in  the  army,  1,033  or  17.5  per  cent,  developed  the  disease.  He 
concludes  that  the  large  number  of  recruits  in  the  camp  certainly  was 
a  factor  in  increasing  the  disease  incidence.  It  should  be  remarked 
that  Camp  Devens  appears  not  to  have  had  any  infiuenza  epidemic 
in  the  spring  of  1918. 

It  is  to  be  regretted  that  we  have  not  several  reports  dealing  with 
the  same  subject  from  camps  where  the  disease  was  definitely  recog- 


AN    p:PIDEMIOLOfJI(;    STUDY  173 

nized  in  the  spring!;.  Fortunatel}''  we  have  one  such.  Opie  and  his 
co-workers  have  observed  that  the  epidemic  at  Camp  Funston,  which 
occurred  between  March  4th  and  March  29th,  1918,  and  which 
attacked  1,127  out  of  a  total  of  29,000  men,  involved  chiefly  the  or- 
ganizations which  had  been  at  Camp  Funston  during  six  months  or 
more.  At  that  time  it  seems  to  have  infected  all  susceptible  individu- 
als, and  to  have  spent  itself.  Subsequent  waves  of  influenza,  four  in 
number,  and  coming  at  a  httle  less  than  one  month  intervals,  occurred 
when  newly  drafted  men  were  brought  into  the  camp  in  April  and  May. 
In  these  latter  cases  the  disease  affected  the  men  newly  arrived  in  camp. 

At  Camp  Funston,  at  least,  the  higher  incidence  in  the  raw  recruit 
appears  to  be  explained  in  part  by  a  relative  immunity  of  those  who 
had  been  in  camp  a  month  or  more,  existing  as  a  result  of  an  earlier 
prevalence  of  the  disease.  More  abundant  evidence  would,  however, 
be  necessary  before  we  could  deny  a  diminution  of  natural  immunity 
in  the  recruits,  caused  by  the  exposure,  overwork,  fatigue,  and  change 
of  daily  routine.  As  V.  C.  Vaughan  has  remarked:  ''It  appears  that 
natural  immunity  gives  way  before  exposure,  overwork  and  fatigue, 
as  was  demonstrated  years  ago  by  Pasteur  in  his  experiments  on  birds 
with  anthrax.  Likewise,  it  is  possible  for  human  beings  to  have  their 
resistance  lowered  by  exposure  to  unaccustomed  environment,  so  that 
although  naturally  immune,  the  standard  of  immunity  is  reduced  to 
the  point  where  the  influenza  virus  gains  admittance  and  overcomes 
the  lowered  resistance." 

Race  stock  and  mortality. — The  relationship  of  morbidity  to  race 
stock  has  already  been  considered  and  should  be  borne  in  mind  in  a 
discussion  of  mortality  by  race. 

We  have  seen  how  the  natives  of  India  suffered  unusually  from  the 
influenza,  the  total  deaths  being  estimated  at  over  5,000,000  individuals. 
A  preliminary  report  from  the  Department  of  the  Interior  on  the 
mortality  from  influenza  among  American  Indians  showed  that 
during  the  six  months  period  from  October  1,  1918,  to  March  31,  1919, 
over  two  per  cent,  of  the  Indian  population  died  of  influenza.  The 
mortality  among  Indians  in  the  Mountain  States,  especially  in  Colo- 
rado, Utah  and  New  Mexico,  was  very  high.  For  the  Indian  popula- 
tion as  a  whole  the  annual  mortality  rate  from  influenza  alone  during 
the  six  months  period  was  according  to  the  U.  S.  Public  Health  Reports 
41.2  per  1,000,  which  is  above  that  for  the  larger  cities  in  the  United 
States  during  the  same  epidemic  period. 

In  both  of  the  above  races  we  cannot  say  that  it  was  not  factors 
other  than  race,  particularly  living  conditions,  that  resulted  in  the 
high  mortality. 


174  INFLUENZA 

Winslow  and  Rogers  found  in  Connecticut  that  the  proportion  of 
influenza-pneumonia  deaths  was  lower  than  would  be  expected  among 
persons  of  native  Irish,  English  and  German  stock,  but  higher  than 
would  be  expected  among  Russian,  Austrian,  Canadian  and  Polish 
stock,  and  enormously  high  among  Italians.  They  suggest  that  this 
marked  difference  in  racial  incidence  may  be  very  largely  due  to  the 
differences  in  age  distribution  of  the  various  race-stocks,  the  races 
showing  the  highest  ratios  being  those  which  have  arrived  more 
recently  in  the  country  and  which  are  made  up  more  largely  of  young 
adults  at  the  ages  which  suffer  most  severely  from  influenza.  They 
further  refer  to  the  work  done  by  Armstrong  in  Framingham,  and 
state  that  their  results  tend  to  confirm  his  conclusions  in  regard  to 
the  Italians,  as  do  the  figures  presented  by  Greenberg  from  the  records 
of  the  Visiting  Nurse  Association  of  New  Haven.  "It  appears  that 
Italy  suffered  very  severely  from  the  influenza  epidemic  in  Europe,  and 
Dublin  has  shown  that  the  normal  pneumonia  rate  of  this  race  is  a  very 
high  one." 

We  have  rather  more  abundant  comparison  of  the  white  and  black 
races  in  this  country.  Frost  found  in  his  extensive  survey  that  the 
case  fatality  was  generally  higher  among  the  colored  than  among  the 
white  population.  A  similar  observation  was  made  by  Howard  and 
Love,  who  found  that  the  case  mortality  for  influenza  and  its  complica- 
tions in  the  United  States  and  in  the  American  Expeditionary  Forces, 
in  1918,  was  for  colored  troops  4.3  per  cent,  and  for  white  troops  3.3. 

These  two  series  of  observations  are  of  great  importance,  for  they  are 
about  all  we  have  describing  case  fatality  rate.  The  majority  of  other 
reports  describe  mortality  rate  only,  and  are  therefore  not  complete. 

The  death  rate  in  the  Army  was  higher  among  colored  troops,  but  the 
incidence  of  influenza,  the  rate  per  1,000,  was  lower  for  the  colored 
race.  "Considering  only  the  southern  states,  the  nativity  rate  for 
influenza  for  the  white  was  247.11  and  for  the  colored,  154,58.  For 
lobar  pneumonia  it  was  10.77  for  the  white  and  28.31  for  the  colored; 
for  bronchopneumonia  and  unclassified  pneumonia  7.26  for  the  whites 
and  11.43  for  the  colored.  It  seems  probable  that  the  negro  is  less 
susceptible  to  influenza  than  the  southern  whites,  but  that  he  is  much 
more  susceptible  to  pneumonic  infections,  either  primary  or 
secondary." 

Frankel  and  Dublin  have  studied  the  racial  distribution  of  70,729 
deaths  among  policy  holders  of  the  Industrial  Department  of  the 
Metropolitan  Life  Insurance  Company,  particularly  with  respect  to 
incidence  among  white  and    black.     Normally   the  mortality  from 


AN    EPIDEMIOLOGIC    STUDY  175 

respiratory  diseases  is  higher  among  colored  persons  than  among 
whites.  In  the  seven  year  period  from  1911  to  1917,  influenza- 
pneumonia  death  rates  showed  an  excess  of  72  per  cent,  colored  males 
over  white  males  and  of  56  per  cent,  colored  females  over  white  females. 
During  the  period  of  the  epidemic  the  situation  was  reversed.  The 
whites  suffered  from  higher  rates  than  the  colored.  While  the  rate 
among  white  males  during  the  period,  October  to  December,  1918,  was 
nearly  fifteen  times  as  great  as  during  the  period  1911  to  1917;  that  of 
colored  males  was  only  seven  times  as  great  as  the  rate  during  the  same 
seven  year  period.  White  females  during  the  height  of  the  epidemic 
showed  a  rate  more  than  sixteen  times  as  high  as  the  normal,  while 
colored  females  experienced  a  rate  only  nine  times  as  high.  After  the 
first  of  January,  1919,  the  excess  rate  returned  slowly  to  the  normal 
figures.     These  facts  are  based  on  death  rate  only. 

Any  comparison  of  race  morbidity  or  mortality,  to  be  of  value, 
must  be  based  on  observations  of  individuals  living  in  the  same  climate, 
in  the  same  domestic  environment,  and  in  similar  age  distribution.  It 
is  practically  impossible  to  discover  groups  living  under  such  condi- 
tions. Howard  and  Love,  perhaps,  approached  more  nearly  to  such 
an  ideal  in  studying  the  white  and  black  races  in  the  Army,  but  even 
in  the  military  forces  many  factors  are  at  play.  Thus,  the  death  rate 
among  enlisted  men  was  highest  among  the  American  troops  in  the 
United  States  (12.02) ;  second  in  Europe  (6.07) ;  third  in  Panama  (1.09) ; 
fourth  in  Hawaii  (0.55);  fifth  in  the  Philippine  Islands  (0.14).  By 
race  it  was  highest  for  the  colored  troops  (12.69) ;  second  for  the  white 
(8.83);  third  for  the  Porto  Ricans  (7.80);  fourth  for  the  Filippinos 
(2.84);  and  fifth  for  the  Hawaiians  (1.72).  The  authors  point  out 
that  while  the  native  troops  had  higher  admission  rates  than  the  whites, 
the  death  rates  were  lower,  which  illustrates  the  point  that  the  death 
rate  for  this  type  of  disease  is  lower  in  the  summer  and  in  the  tropics. 

SECTION  IV. 

An  Intensive  Study  of  the  Spread  of  Influenza 

IN  Small  Groups  of  Closely  Associated 

Individuals. 

We  have  been  discussing  the  disease  under  consideration  chiefly 
from  the  viewpoint  of  the  statistician.  The  statistician,  possessing 
a  wealth  of  information  of  a  general  nature,  and  from  all  parts  of  the 
world,  and  armed  with  fascinating  complex  mathematical  instruments, 
is  able  to  dissect  the  information  at  his  disposal,  and  to  reconstruct 


176  INFLUENZA 

therefrom  both  facts  and  apparent  facts  of  absorbing  interest.  To 
him  we  are  indebted  for  the  bulk  of  our  knowledge  of  the  distribution 
and  spread  of  the  influenza  through  metropolies,  through  countries, 
and  through  continents. 

Like  the  aviator  flying  over  enemy  territory  he  acquires  a  breadth 
of  vision  and  a  general  perspective  which  is  to  a  great  extent  denied  to 
those  remaining  on  the  ground.  But  also  like  the  aviator,  from  the  very 
fact  of  his  high  position  he  loses  the  ability  to  recognize  detail.  The 
small  sub-divisions  in  the  enemy  lines  are  slightly  blurred  and  he  can 
distinguish  the  front  line  trenches  in  which  most  of  the  action  is  occur- 
ring no  more  clearly  than  the  reserve  and  support  trenches.  An  Army 
depending  entirely  upon  its  aeroplane  reconaissance  would  find  itself 
helpless  in  combatting  the  enemy.  The  aeroplane  is  useful,  yes,  it 
could  not  be  dispensed  with,  but  never  an  opportunity  is  lost  for 
scouting  parties  to  explore  the  enemy  front  lines;  it  is  these  latter  who 
bring  back  information  as  to  the  local  strength  and  distribution  of  the 
enemy,  as  to  what  particular  divisions  are  in  action,  as  to  the  strength 
of  the  entrenchments,  the  enemy  distribution  within  the  trenches, 
and  finally  what  is  most  important,  information  as  to  the  weak  points 
in  the  enemy's  lines,  places  at  which  we  may  concentrate  our  attack 
with  the  hope  of  driving  the  enemy  from  its  stronghold.  Occasionally 
a  raiding  party  will  return  with  a  prisoner.  He  will  be  examined 
thoroughly  and  may  yield  some  valuable  information.  All  such 
prisoners  are  not  dressed  alike.  We  recognize  that  some  belong  to  one 
regiment  and  some  to  another.  After  we  have  extracted  what  infor- 
mation we  can  from  the  prisoner  he  is  incarcerated,  if  we  may  extend 
our  metaphor,  in  a  test  tube,  and  there  he  remains  for  future  reference. 
We  do  not"  believe  that  these  individual  private  soldiers  are  the  cause  of 
the  war,  but  we  do  know  that  they  are  doing  their  share  of  the  killing — 
that  they  are  doing  most  of  the  killing. 

It  is  characteristic  of  human  enthusiasm  and  hopefulness  that  each 
raiding  party  prays  that  it  may  bring  back  with  it  a  general  ofl&cer,  a 
field  marshall,  the  one  who  is  chiefly  responsible  for  the  enemy  offen- 
sive. In  our  own  little  battle  with  our  invisible  host  we  have  long 
since  discovered  that  field  marshalls  here  as  elsewhere  are  difficult  to 
discover  by  raiding  parties.  But  the  raids  are  and  should  be  made  just 
the  same.  They  almost  invariably  bring  back  some  new  item  of  infor- 
mation, and  it  is  the  experience  of  many  wars  that  even  though  the 
commanding  general  be  never  captured,  repeated  small  or  large 
attacks  following  preliminary  reconaissance,  if  diligently  and  valiantly 
prosecuted  under  good  leadership  may  win  the  war. 


AN    EPIDEMIOLOGIC    STUDY 


177 


In  studying  the  life  and  habits  of  the  influonza  virus  and  its  army 
of  secondary  invaders,  and  the  results  thereof  in  small  groups  composed 
of  individuals  as  the  unit,  instead  of  large  groups  with  communities 
as  a  unit,  we  will  be  able  to  discover  a  certain  number  of  additional 
facts,  some  of  which  may  have  considerable  value. 

In  the  study  by  the  author  of  six  selected  districts  in  Boston  a 
special  study  was  made  of  the  occurrence  and  manner  of  spread  of  the 
influenza  in  the  household  or  family  as  a  unit.  The  10,000  individuals 
canvassed  were  distributed  through  2,117  families.  Of  these  two 
thousand  odd  families,  45.44  per  cent,  were  visited  with  one  or  more 
cases  of  the  disease  in  the  1918-19  epidemic,  and  27.25  per  cent,  in 
the  winter  of  1920.  Of  these,  14.31  per  cent,  had  cases  in  both  epi- 
demics. In  either  one  or  both  of  the  two  epidemics  under  considera- 
tion, 58.38  per  cent,  of  all  families  had  influenza  (see  Table  III). 

TABLE  III. 
Per  cent,  of  families  invaded  by  influenza. 


Boston  District 
No. 

1918-19. 

1920. 

1918-19  and 
1920. 

Total. 

1 

49.59 

32.79 

20.05 

62.33 

2 

36.04 

17.36 

7.25 

46.15 

3 

45.89 

26.43 

14.71 

57.61 

4 

48.48 

32.20 

14.39 

66.29 

5 

52.48 

34.11 

19 .  53 

67.06 

6 

43.16 

24.21 

11.23 

56.14 

All  Districts 

45.44 

27.25 

14.31 

58.38 

Explanatory  note:  45.44  per  cent,  of  all  families  were  invaded  in|^1918. 
27.25  per  cent,  of  all  families  were  invaded  in  1920. 
14.31  per  cent,  of  all  families  were  invaded  in  both  epidemics. 
58 .  38  per  cent,  of  all  families  were  invaded  in  one  or  the  other 

or  both. 
41 .  62  per  cent,  of  all  families  remained  free  from  influenza 
throughout  both  epidemics. 


In  this  discussion  of  family  incidence,  as  in  our  work  on  the  inci- 
dence among  individuals,  the  question  naturally  arises  as  to  the 
reliability  of  our  information  and  the  accuracy  of  our  results.  We 
have  shown  the  close  correspondence  between  our  own  results  and 
those  of  Frost,  done  on  a  vastly  larger  number  of  individuals.  The 
information  for  families  was  obtained  from  the  same  sources  and  from 
the  same  individuals.  The  thoroughness  with  which  the  inspectors 
did  their  work  is  indicated  by  the  fact  that  in  addition  to  the  2,117 
families  on  which  we  base  our  results,  only  the  records  of  194  families 


178  INFLUENZA 

have  been  discarded  for  various  reasons.  In  discarding  the  family 
records  we  also  discarded  the  individual  records  and  such  are,  there- 
fore, for  individuals  above  our  total  of  10,000.  One  hundred  and  fifty- 
four  of  these  were  for  families  whose  homes  were  in  the  districts 
surveyed,  but  who  were  not  at  home  at  the  time  of  the  first  survey. 
These  were  omitted  during  the  second  survey,  irrespective  of  whether 
individuals  were  at  home.  In  this  group  are  also  included  a  few  in 
which  children  were  at  home,  but  were  unable  to  give  reliable  informa- 
tion. Fifteen  of  the  194  families  gave  insufficient  information,  and  25 
refused  to  co-operate.  The  small  number  in  this  last  group  speaks 
well  for  the  efficiency  and  methods  of  the  inspectors.  All  families 
accepted  for  tabulation  co-operated  to  the  best  of  their  ability^  and 
we  believe  that  the  records  are  as  accurate  as  this  type  of  work  may  be 
made. 

Dr.  Niven,  in  the  work  referred  to  by  Carnwath,  made  an  inquiry 
covering  1,021  houses,  with  a  population  of  4,721.  Five  hundred  and 
three  households  or  almost  exactly  one-half,  were  invaded  in  either  the 
summer  1918,  or  the  autumn-winter  1918  epidemic.  This  proportion 
of  families  is  quite  similar  to  our  own,  but  it  must  be  pointed  out  that 
Niven  was  not  studying  the  same  two  epidemics  that  we  are  discussing. 
Two  hundred  and  sixty-six  of  his  total  households,  or  26.05  per  cent, 
were  invaded  in  the  autumn  epidemic. 

Previous  to  the  present  time  the  author  has  been  unable  to  find 
records  of  investigators  having  used  this  method  of  studying  influenza 
to  any  appreciable  extent.  Certainly  there  has  been  nothing  done 
on  the  subject  previous  to  the  last  pandemic.  Since  then  Frost  has 
studied,  as  indicated  in  his  report,  family  incidence  to  the  extent  of 
determining  the  relationship  to  overcrowding  and  to  economic  status, 
and  Niven  has  studied  family  incidence  with  special  reference  to 
immunity. 

Thomas  Sydenham,  speaking  of  the  epidemic  of  1675,  says  that: 
"No  one  escaped  them  whatever  might  be  his  age  or  temperament, 
and  they  ran  through  whole  families  at  once." 

According  to  Waldschmidt,  during  the  epidemic  of  1712,  in  Kiel, 
ten  or  more  persons  were  frequently  taken  ill  in  one  house. 

In  1732,  Huxam  tells  us  that,  "not  a  house  was  free  from  it,  the 
beggar's  hut  and  the  nobleman's  palace  were  alike  subject  to  its  attack, 
scarce  a  person  escaping  either  in  town  or  country,  old  and  young, 
strong  and  infirm,  shared  the  same  fate." 

Metzger  says  that  the  influenza  was  so  universal  in  March,  1782, 
that  in  very  many  houses  all  of  the  inmates  were  attacked.     On  the 


AN    EPIDEMIOLOGIC    STUDY  179 

other  hand,  Mertens  did  not  beUeve  the  influenza  a  contagion  during 
the  same  epidemic  for  the  reason  that  according  to  his  observations 
now  only  one,  and  again  all,  of  the  members  of  a  family,  were  stricken. 

In  1833,  in  Konigsberg,  according  to  Hufeland,  parents,  children, 
and  servants  were  frequently  smitten  with  the  disease  at  the  same  time, 
so  that  strange  help  had  to  be  obtained  for  the  family. 

Parkes  taught  that,  ''Persons  in  overcrowded  habitations  have, 
particularly  in  some  epidemics,  especially  suffered,  and  several  in- 
stances are  on  record  of  a  large  school  or  a  barrack  for  soldiers  being 
first  attacked,  and  of  the  disease  prevailing  there  for  some  days  before 
it  began  to  prevail  in  the  town  around.  Sometimes,  on  the  other  hand, 
schools  and  prisons  have  escaped.  A  low,  damp,  ill-ventilated  and  un- 
healthy situation  appears  to  predispose  to  it,  and  in  some  instances,  in 
hospital  patients,  it  has  assurned  a  malignant  character.  In  other 
cases  again,  hospital  patients  have  escaped;  for  example,  the  old 
people  in  the  Salpetri^re  in  1837,  when  the  younger  attendants  were 
attacked." 

Effect  of  overcrowding. — The  family  or  household  forms  a  social 
unit  in  which  human  intercourse  is  very  close,  and  in  which  the 
opportunities  for  contact  infection  either  direct  or  indirect  are  mani- 
fold. In  addition  to  all  of  the  opportunities  which  each  individual 
has  for  contracting  the  disease  outside  of  the  family  every  case  in  the 
family  exposes  every  other  member  many  times  during  the  day.  One 
of  the  first  questions  arising  in  a  study  of  the  disease  in  the  family  is, 
therefore,  whether  the  size  of  the  family  in  and  of  itself  exerts  any 
predisposing  influence  on  the  total  incidence  in  any  one  family.  Are 
large  families  more  likely  to  have  a  greater  percentage  of  cases 
than  small  families?  We  have  endeavored  to  answer  this  question  by 
grouping  together  all  famihes  containing  only  one  individual,  all  of 
those  with  two,  three,  four,  etc.,  and  determining  the  percentage  of 
individuals  contracting  influenza  in  each  of  the  groups.  The  standard 
for  comparison  is  the  percentage  of  the  total  10,000  who  contracted 
the  disease  in  either  year,  or  in  both.  19.71  per  cent,  of  all  persons 
canvassed  contracted  influenza  in  1918-19.  Reference  to  Table  IV 
shows  that  of  persons  living  in  families  of  one,  17.95  per  cent,  developed 
the  disease;  of  those  in  families  of  two,  18.46  per  cent.;  in  families  of 
three,  19.96  per  cent.;  in  families  of  four,  20.10  per  cent.;  and  in 
families  of  from  five  to  seven,  between  22  and  23  per  cent.  Families 
of  over  seven  all  showed  lower,  but  varying  incidence  of  the  disease. 
As  is  seen  by  the  table,  they  comprise  only  a  small  number  of 
families. 

15 


180  INFLUENZA 

TABLE  IV. 

The  incidence  of  influenza  in  families  of  different  sizes. 
(Influence  of  size  of  family). 


No.  of 

such 

families. 

Total  No.  of 
individuals  in- 
cluded in  all 

Number  of  these  individuals  who  developed 
influenza. 

viduals  in 
family. 

1918. 

1920. 

Total. 

No. 

Per  cent. 

No. 

Per  cent. 

No. 

Per  cent. 

1 

39 

39 

7 

17.95 

3 

7.69 

10 

24.42 

2 

260 

520 

96 

18.46 

55 

10.58 

151 

29.04 

3 

359 

1077 

215 

19.96 

128 

11.88 

343 

31.85 

4 

396 

1584 

319 

20.10 

169 

10.67 

488 

30.81 

5 

375 

1875 

423 

22.56 

203 

10.83 

626 

33.39 

6 

264 

1584 

361 

22.79 

151 

9.53 

512 

32.32 

7 

179 

1253 

279 

22.27 

109 

8.70 

388 

30.96 

8 

103 

824 

156 

18.93 

55 

6.67 

211 

25.61 

9 

57 

513 

85 

16.57 

21 

4.09 

106 

20.66 

10 

28 

280 

40 

14.14 

26 

9.29 

66 

23.57 

11 

15 

165 

10 

6.06 

7 

4.24 

17 

10.30 

12 

4 

48 

0 

0.0 

5 

10.42 

5 

10.42 

13 

2 

26 

5 

19.23 

3 

11.54 

8 

30.77 

14 

1 

14 

0 

0.0 

0 

0.0 

0 

0.0 

In  1920,  9.55  per  cent,  of  the  entire  canvassed  population  con- 
tracted the  disease.  The  table  shows  that  7.69  per  cent,  of  all  indivi- 
duals in  families  of  one  contracted  influenza,  and  between  10  and  12 
per  cent,  in  families  of  from  two  to  five  individuals.  Above  the  family 
of  five  the  incidence  rates  again  are  lower  and  varying  within  wide 
limits.  The  last  column  shows  the  percentage  of  individuals  by  size 
of  family  contracting  the  disease  in  either  or  both  epidemics. 

The  average  size  of  all  families  was  4.7  individuals. 

If  we  consider  only  those  family  groups  having  over  1,000  indivi- 
duals as  being  sufficiently  large  to  be  representative,  we  may  conclude 
that  families  of  from  three  to  seven  individuals  show  no  progressive 
increase  in  influenza  incidence  with  increase  in  size  of  the  family. 
But  all  the  available  evidence  indicates  that  other  things  being  equal, 
the  age  incidence  is  a  very  important  factor.  Its  influence  will  be 
felt  in  the  subject  under  consideration,  and  it  will  modify  the  results. 
Thus,  families  of  one  or  two  are  almost  invariably  adults;  families  of 
three  are  very  frequently  made  up  of  two  adults  and  a  child  or  infant, 
while  families  of  from  five  to  seven  will  be  more  likely  to  have  a  high 
proportion  of  young  adults — the  age  period  more  seriously  affected. 

The  next  question  arising  is  whether  those  families,  large  or  small, 
which  are  living  in  crowded  circumstances,  are  more  likely  to  develop 


AN    EPIDEMIOLOGIC    STUDY  181 

the  disease.  Arbitrary  standards  must  be  chosen  as  indices  of  crowd- 
ing. We  have  chosen  two  in  order  that  they  may  check  each  other. 
The  first  is  based  upon  the  number  of  individuals  sleeping  in  a  bed- 
room. Families  are  classified  as  follows:  Maximum  sleeping  in  a 
single  bedroom,  1 ;  maximum  sleeping  in  a  single  bedroom,  2;  maximum 
per  bedroom,  3,  4,  etc. 

The  second  standard  of  crowding  is  based  upon  the  ratio  of  the 
number  of  individuals  in  the  family  and  the  number  of  rooms  occupied. 
One  person  living  in  one  room  is  not  crowded ;  two  in  two  rooms,  three  in 
three  rooms,  four  in  four  rooms,  eight  in  eight  rooms,  twelve  in  twelve 
rooms,  are  not  crowded.  Two  people  living  in  one  room  four  in  two 
rooms,  six  in  three  rooms,  twelve  in  six  rooms,  are  decidedly  more 
crowded.  On  the  contrary,  one  individual  in  two  rooms,  two  in  four, 
three  in  six,  four  in  eight,  five  in  ten,  etc.  have  an  unusual  amount  of 

room. 

p 
The  ratios  ware  then  throughout,  \,  |,   §.     These  are  used  as 

dividing  lines.  All  families  with  ratios  higher  than  f  are  classed  as 
very  crowded.  Families  with  ratios  above  [  up  to  and  including  i  are 
classed  as  crowded.  Families  with  ratios  above  |  up  to  and  including 
1  are  classed  as  roomy,  and  those  with  ratio  of  ^  or  lower  are  classified 
as  very  roomy. 

Classif3dng  all  families  in  all  six  districts  according  to  these  last 
four  degrees  of  crowding,  we  find,  as  is  shown  by  Table  V,  that  there  is 
a  progressive  increase  in  the  proportion  of  families  with  one  or  more 
cases  of  the  disease,  with  increase  in  the  extent  of  crowding. 

According  to  the  standard  first  described  we  find  as  is  shown  in 
Table  VI  that  families  with  three,  four  and  five  individuals  sleeping  in  a 
single  room  show  a  progressive  increase  of  incidence  over  those  families 
with  but  one  or  two  per  bedroom.  This  again  is  shown  best  in  the 
total  for  all  families,  but  is  borne  out  in  a  study  of  each  district.  These 
statistics  are  however  of  little  value  for  the  study  of  the  effect  of 
overcrowding,  because  crowded  families  are  usually  large  families. 
With  an  influenza  incidence  of  20  per  cent,  we  would  theoreticall}^ 
expect  every  family  of  five  or  larger  to  have  one  or  more  cases.  This 
would  amount  to  100  per  cent,  infected  families  and  such  a  state  would 
not  only  influence,  but  dominate  the  statistics  regarding  overcrowding. 

An  objection  will  be  raised,  and  justly  so,  that  we  have  up  to  this 
point  been  studying  influenza  in  families  irrespective  of  how  many 
cases  there  are  in  each  family.  Until  now  the  family  with  one  case 
was  classified  exactly  the  same  as  the  family  with  eight  cases.     In  the 


182 


INFLUENZA 


TABLE  V. 

Effect  of  crowding  on  development  of  infliienza  in  families. 
(A  higher  proportion  of  crowded  households  than  roomy  are  invaded). 
(Standard  used:  ratio  of  number  individuals  to  number  rooms). 


ving  conditions. 

No.  of  such 
families. 

Proportion  of  these  families  visited  by  influenza. 

Li 

In  1918-19. 

In  1920. 

In  both 

epidemics 

(Recurrent). 

Total  families 
invaded. 

No. 

Per 
cent. 

No. 

Per 
cent. 

No. 

Per 

cent. 

No. 

Per 

cent. 

V.  Cr 

District  I. 

53 

195 
79 
16 

30 

107 

36 

7 

56.61 
54.87 
45.57 
43.75 

15 

59 

24 

1 

28.31 

30.26 

30.38 

6.6 

12 

43 

18 

0 

22.64 

22.05 

22.78 

0.0 

31 

123 

42 

8 

58  49 

Cr 

63  08 

R 

53  16 

V.  R 

50  00 

V.  Cr. 

District  II. 

4 
137 
208 
103 

1 
70 
70 
20 

25.00 
51.09 
33.65 
19.42 

1 
31 
39 

7 

25.00 

22.63 

18.75 

6.80 

1 
2 
7 
2 

25.00 
8.76 
8.17 
1.94 

1 
89 
92 
25 

25  00 

Cr 

64  96 

R 

44  23 

V.  R 

24  27 

V.  Cr 

District  III. 

13 
213 
143 

21 

9 
99 
62 

8 

69.23 
46.48 
43.36 
27.59 

2 

65 

35 

2 

15.38 

30.52 

24.48 

6.89 

1 
40 
15 

2 

7.69 
18.78 
10.49 

6.89 

10 
124 

82 
8 

76  92 

Cr 

58  22 

R 

57  34 

V.  R 

38  09 

V.  Cr. 
Cr. . . . 
R 

District  IV. 

0 

27 

137 

95 

0 

18 
72 
38 

66!  67 
52.55 
40.00 

0 

8 
50 
27 

29!  63 
36.49 
28.42 

0 

5 

21 

12 

is!  52 
15.33 
12.63 

0 

21 

101 

53 

77!  77 
73  72 

V.  R. 

55.79 

V.  Cr. 

District  V. 

6 

110 

209 

14 

2 

67 

104 

3 

33.33 

60.91 
49.76 
21.42 

4 
37 
70 

3 

66.67 
33.64 
33.49 
21.42 

2 
25 

33.33 

22    7R 

4 

79 

146 

6 

66  67 

Cr 

71  82 

R 

38     1    IS   IS 

69  86 

V.  R 

0 

42.84 

V.  Cr. 

District  VI. 

0 

2 

92 

189 

0 

1 
57 
65 

56!  66 

61.96 
34.39 

0 

0 

23 

46 

6;6' 

25.00 
24.34 

0 

0 

14 

"6!6' 

15.22 

0 

1 
66 
92 

Cr 

50  GO 

R 

71  74 

V.  R 

19 

10.05 

48.68 

Living 
conditions. 

No.  of 
families. 

No. 

1918. 

Per 

cent. 
1918. 

No. 
1920. 

Per 
cent. 
1920. 

No. 
both. 

Per 
cent, 
both. 

Total 

Per 

cent. 

Very  crowded 

Crowded 

Roomy 

Very  Roomy 

80 
693 
865 
443 

43 
372 
394 
143 

53.75   1         25 
53.68   :     201 
45.55   I     244 
32.28   1        87 

31.25 
29.00 
28.21 
19.64 

18 
126 
125 

36 

22.50 

18.18 

14.45 

8.13 

50 
447 
513 
194 

62.50 
64.50 
59.31 
43.79 

All 

Total          1918 

Per          1920 
cent.    1 

Per 
cent. 

Both 

Per 

cent. 

Total 

Per 
cent. 

2081              952 

45.75 

5.57 

26.77         305         14.66        1204     ;   57.86 

AN    EPIDEMIOLOGIC    STUDY 


183 


TABLE  VI. 

Effect  of  crowding. 
(Standard  used:  maximum  number  sleeping  in  one  bed  room.) 


Maximum  No. 

sleeping  per 

room. 

No.  of 

such 
families. 

Proportion  of  these  families  with  caaes  of  influenza . 

In 

1918-19. 

I 

Q  1920. 

In  both  epi- 
demics. 

Total  families 
invaded. 

No. 

Per  cent. 

No. 

Per  cent. 

No. 

Per  cent. 

No. 

Per  cent. 

District  I. 

1 

16 

6 

37.50 

4 

25.00 

3 

18.75 

7 

93.75 

2 

93 

52 

55.91 

31 

33.33 

20 

21.51 

63 

67.74 

3 

145 

65 

44.83 

47 

32.41 

27 

18.62 

85 

58.62 

4 

79 

43 

54.43 

25 

31.65 

17 

21.52 

51 

64.56 

5 

24 

11 

45.83 

11 

45.83 

6 

25.00 

16 

66.67 

6 

10 

3 

30.00 

3 

30.00 

1 

10.00 

5 

50.00 

District  II. 

1 

90 

15 

16.67 

7 

7.77 

2 

2.22 

20 

22.22 

2 

211 

68 

32.23 

36 

17.06 

14 

6.64 

90 

42.65 

3 

115 

59 

51.30 

23 

20.00 

10 

8.69 

72 

66.61 

4 

33 

20 

60.60 

11 

33.33 

6 

18.18 

25 

75.76 

o 

3 

1 

33.33 

2 

66.67 

1 

33.33 

2 

66.67 

6 

0 

0 

0 

0 

0 

District  III. 

1 

26 

10 

38.46 

3 

11.54 

2 

7.69 

11 

42.31 

2 

179 

73 

40.78 

47 

26.26 

23 

12.85 

97 

54.19 

3 

145 

72 

49.66 

37 

25.52 

23 

15.86 

86 

59.31 

4 

39 

20 

51.28 

15 

38.46 

8 

20.51 

27 

69.23 

0 

8 

5 

62.50 

2 

25.00 

1 

12.50 

6 

75.00 

6 

0 

0 

0 

0 

0 

District  IV. 

1 

53 

15 

28.30 

15 

28.30 

6 

11.32 

24 

45.28 

2 

165 

80 

48.48 

56 

33.94 

22 

13.33 

114 

69.09 

3 

♦42 

29 

69.05 

15 

35.71 

10 

23.81 

34 

80.95 

4 

5 

4 

8.00 

0 

0.0 

0 

0.0 

4 

80.00 

5 

0 

0 

0 

0.0 

0 

0 

6 

0 

0 

0 

0 

0 

District  V. 

1 

23 

8 

34.77 

6 

26.08 

1 

4.35 

13 

56.52 

2 

156 

70 

44.37 

48 

30.77 

24 

15.38 

94 

60.26 

3 

130 

81 

62.31 

44 

33.84 

27 

20.77 

98 

75.38 

4 

27 

18 

66.66 

14 

51.85 

12 

44.44 

20 

74.07 

5 

6 

3 

50.00 

4 

66.67 

3 

50.00 

4 

66.67 

6 

1 

0 

0.00 

0 

0.00 

0 

0.00 

0 

0.00 

District  VI. 

1 

120 

42 

35.00 

24 

20.00 

10 

8.33 

66 

46.67 

2 

146 

77 

52.74 

34 

23.29 

22 

15.07 

89 

60.96 

3 

10 

5 

50.00 

5 

50.00 

1 

10.00 

6 

60.00 

4 

0 

0 

0 

0 

0 

5 

0 

0 

0 

0 

0 

C 

0 

0 

0 

0 

0 

Total 

1 

328 

96 

29.27 

59 

17.99 

24 

7.32 

131 

39.94 

2 

450 

420 

44.21 

252 

26.53 

125 

13.16 

547 

57.57 

3 

587 

311 

52.98 

171 

29.13 

98 

16.69 

.^81 

64.91 

4 

183 

105 

57.38 

65 

35.52 

43 

23.50 

127 

69.39 

5 

41 

20 

48.78 

19 

46.34 

11 

26.83 

28 

68.29 

6 

11 

3 

27.27 

3 

27.27 

1 

9.09 

5 

45.45 

184  INFLUENZA 

following  classification  we  have  taken  first  all  families  with  a  maximum 
of  one  sleeping  in  one  room,  and  sub-divided  these  into  families  with 
no  influenza,  those  with  one  case,  two  cases,  etc.  We  have  likewise 
classified  families  with  maxima  from  two  to  six  per  bedroom.  For  the 
sake  of  brevity  we  will  consider  only  the  last  column  of  Table  VII, 
influenza  incidence  among  the  individuals  of  the  various  classes  of 
families  for  both  epidemics.  Study  of  the  table  will  show  a  correspond- 
ence in  the  other  columns.  Solitary  cases  were  more  numerous  in 
families  with  but  one  or  two  per  bedroom  (27  per  cent.)  and  less 
frequent  in  families  with  three,  four  and  five  per  bedroom,  (23  per 
cent.,  18  per  cent.,  and  20  per  cent.,  respectively).  The  families  of 
six  per  bedroom  form  such  a  small  group  that  here  again  they  should 
not  be  considered.  Multiple  cases  become  progressively  more  numer- 
ous as  the  number  of  individuals  per  bedroom  increases  (14  per  cent, 
in  families  of  one  per  bedroom,  29  per  cent,  in  two  per  bedroom,  41 
per  cent,  in  three,  51  to  52  per  cent,  in  four,  and  45  per  cent,  in  five). 
Fifty-eight  per  cent,  of  families  with  a  maximum  of  one  per  bedroom, 
43  per  cent,  with  two  per  bedroom,  35  per  cent,  with  three,  31  per  cent, 
with  four  and  35  per  cent,  with  five  had  no  influenza  at  all. 

But  here  again,  the  fact  that  crowded  families  are  usually  large 
families  interferes  with  drawing  any  conclusions.  A  family  with  four 
per  bed  room  would  generally  be  larger  than  one  with  two  per  bed 
room. 

Frost  observed  that,  considering  the  ratio  of  incidence  in  total 
white  populations  irrespective  of  housing  as  100,  and  after  adjusting 
all  groups  to  a  uniform  sex  and  age  distribution,  the  ratio  where  there 
were  more  than  1.5  rooms  per  person  was  77,  from  1  to  1.5  rooms  per 
person  the  ratio  was  94,  and  for  individuals  averaging  less  than  one 
room  per  person  it  was  117.  The  attack  rate  showed  a  consistent 
increase  as  the  number  of  rooms  per  person  decreased. 

Woolley  observed,  "Housing,  if  one  includes  in  the  term  over- 
crowding, has  surely  been  an  important  factor  in  spreading  the  epi- 
demic. Whether  it  has  had  any  appreciable  effect  upon  the  incidence 
of  complications  is  a  question.  The  epidemic  has  certainly  gone  faster 
and  was  over  sooner  because  of  the  crowding;  the  hospital  was  filled 
sooner  than  it  should  have  been  as  a  result  of  the  rapidity  of  spread 
of  the  disease,  and  overcrowding  of  the  hospital  occurred  when  with  a 
less  rapid  spread  it  would  not  have  occurred;  but  whether  the  number 
of  fatalities  or  the  number  of  pneumonias  was  greater  than  they  should 
have  been  with  less  crowded  conditions  may  be  doubted." 


AN    EPIDEMIOLOGIC    STUDY 


185 


TABLE  VII. 

Relationship  between  crowding  and  number  of  cases  in  the  family. 

(Influenza  appeared  more  frequently  in  crowded  households  and  such  families 

more  frequently  had  multiple  cases.) 

Families  with  maximum  per  bed  room  of  one. 
(68.23  per  cent,  of  these  had  no  influenza.) 


Invaded  in 

Invaded  in 

Invaded  in 

both 
epidemics. 

Total  fami- 

Two or 

Cases  dc- 

Total 

1918-19. 

1920. 

lies  invaded. 

more  cases. 

velopiiiR    in 

such 
families. 

family. 

No. 

Per 
cent. 

No. 

Per 
cent. 

No. 

Per 
cent. 

No. 

Per 
cent. 

Per  cent. 

1 

8.5 

55 

17.68 

37 

11.89 

7 

2.25 

311 

27.33 

2 

32 

26 

8.36 

16 

5.14 

10 

3.22 

10.28 

1 

3 

9 

8 

2.57 

2 

0.64 

1    1     0.32 

...    !      2.88 

\    14.44 

4 

4 

3 

0.96 

4 

1.28 

3 

0.96 

1.28 

1 

o 

0 

0 

6 

0 

7 

0 

8 

0 

2  per  bed  room. 
(43.35  per  cent,  of  these  had  no  influenza.) 


254 

135 

79 

40 

11 

3 

2 

0 


169 

18.27 

112 

12.11 

27 

2.92 

925 

27.46 

112 

12.11 

64 

6.92 

41 

4.43 

14.59      1 

65 

7.03 

38 

4.11 

24 

2.59 

8.. 54 

35 

3.78 

16 

1.73 

11 

1.18 

4.32      1 

9 

0.97 

8 

0.81 

6 

0.64 

1.18 

3 

0.32 

0 

0.0 

0 

0.0 

0.32 

2 
0 

0.22 

1 

0.11 

1 

0.11 

0.22      J 

3  per  bed  room. 
(35.34  per  cent,  of  these  had  no  influenza.) 


136 

103 

59 

43 

22 

12 

2 

0 


104 

17.84 

50 

8.58 

18 

3.08 

583 

23.33 

77 

13.21 

55 

9.43 

29 

4.97 

17.67 

51 

8.75 

29 

4.97 

21 

3.60 

10.12 

40 

6.86 

16 

2.76 

13 

2.23 

7.37 

22 

3.77 

9 

1.54 

9 

1.54 

3.77 

12 

2.06 

5 

0.86 

5 

0.86 

2.06 

2 

0.34 

0 

0 

0.34 

41.33 


4  per  bed  room. 
(30.79  per  cent,  of  these  had  no  influenza.) 


1 

31 

24 

13.64 

10 

5.68 

3 

1.70 

176 

17.61 

2 

22 

19 

10.80 

13 

7..S9 

10 

5.68 

12.50 

3 

37 

32 

18.18 

25 

14.20 

20 

11.36 

20.92 

4 

14 

11 

6.25' 

6 

3.41 

3 

1.70 

9.09 

51.60 

0 

9 

9 

5.12 

4 

2.27 

4 

2.27 

5.12 

6 

4 

3 

1.70 

2 

1.19 

1 

0.59 

2.27 

7 

3 

3 

1.70 

0 

0 

1.70 

8 

0 

(35  per 


5  per  bed  room, 
per  cent,  had  none.) 


6 

15.00 

4 

10.00 

2 

5.00 

10 

20.00 

5 

12.50 

4 

10.00 

3 

7.25 

15.00 

2 

5.00 

2 

5.00 

1 

2.50 

7.50 

1 

2.50 

2 

5.00 

1 

2.50 

5.00 

2 

5.00 

3 

7.50 

1 

2.50 

10.00 

2 

5.00 

2 

5.00 

2 

5.00 

5.00 

"6 

0.0 

"i 

'2.'56 

'  '6 

0.0 

'2!  50 

45.00 


6  per  bed  room. 
(50  per  cent,  had  none.) 


1 

10.00 

1 

10.00 

0 

0.0 

10 

20.00 

1 

10.00 

1 

10.00 

1 

10.00 

10.00 

1 

10.00 

1 

10.00 

■ 

0 

0.0 

20.00 

30.00 


186  ^  INFLUENZA 

The  housing  methods  in  the  cantonments  and  even  in  the  tent 
camps  resulted  in  a  degree  of  congestion  and  close  physical  contact 
among  individuals  that  was  attained  in  no  civil  communities  with  the 
possible  exception  of  some  institutions.  In  cantonments  the  number 
of  men  in  individual  rooms  ranged  from  30  to  100  and  even  under  the 
best  circumstances  there  was  very  evident  close  crowding.  An  indi- 
vidual in  any  of  these  large  rooms  contracting  a  contagious  disease 
had  opportunities  to  spread  it  by  contact  and  by  droplet  infection  not 
only  to  one  or  two  others,  as  in  the  case  of  the  average  family,  but  to  a 
large  group  of  the  men  in  the  same  room.  A  vicious  circle  was  thus 
formed  which  tended  to  propagate  the  disease  throughout  any  camp 
with  utmost  rapidity.  Brewer  has  compared  the  influenza  incidence 
rate  in  the  principal  white  organizations  at  Camp  Humphreys  with 
the  floor  space  allowed  each  man  in  the  respective  organizations,  and 
concludes  that,  "It  is  not  proper  or  just  to  attribute  the  differences 
shown,  alone  to  the  amount  of  floor  space  allowed  each  organization, 
but  it  certainly  points  very  strongly  to  the  fact  that  the  incidence  of 
the  disease  varied  with  the  density  of  the  population,  although  not 
with  mathematical  regularity,"  Brewer  cites  regiments  which  al- 
though housed  alike  showed  definite  variation  in  the  influenza  inci- 
dence. This  merely  shows  that  other  factors  also  play  a  part.  Thus, 
in  one  instance,  the  difference  in  the  two  regiments  was  in  length  of 
service.  Brewer  also  found  that  among  the  white  troops  the  incidence 
of  pneumonia  appears  to  vary  with  the  density  of  the  population. 

V.  C.  Vaughan  has  reported  on  the  relationship  between  incidence 
in  tents  and  in  barracks  at  Camp  Custer.  From  this  one  observation 
it  would  appear  that  the  incidence  is  little  changed  under  the  two 
conditions. 

"During  September  and  October,  1918,  a  study  was  made  on  the  re- 
lationship, if  any,  of  influenza  to  methods  of  living.  Of  the  command, 
3,633  were  in  tents.  The  morbidity  per  thousand  in  these  was  129. 
There  were  in  barracks  36,055.  The  morbidity  per  thousand  among 
those  was  275.  At  first  glance  the  lower  morbidity  of  those  in  tents 
is  striking,  but  going  further  into  the  matter  it  was  found  that  the 
entire  morbidity  of  the  Quartermaster  Corps  was  very  low.  Of  the 
Depot  Brigade  2,881  were  in  tents,  with  a  morbidity  of  128  per  thou- 
sand, while  3,824  were  in  barracks,  with  a  morbidity  of  134  per 
thousand." 

Howard  and  Love  offer  three  reasons  why  during  the  last  four 
months  of  1918  the  deaths  from  influenza  and  pneumonia  in  the 
Army  in  the  United  States  ran  at  a  rate  nearly  three  times  as  high  as 


AN    EPIDEMIOLOGIC    STUDY  187 

that  among  our  troops  in  France:  First,  that  the  troops  in  the  United 
States  were  recent  recruits  and  therefore  more  susceptible  to  disease; 
second,  that  probably  many  of  the  troops  in  France  who  had  seen 
much  longer  service  had  had  the  disease  in  mild  form  in  the  early 
spring;  and,  third,  that  the  method  of  housing  was  entirely  different 
in  France.  There  the  men  were  spread  over  a  wide  territory  and 
whenever  in  rest  area  they  were  billeted  in  houses  rather  than  crowded 
into  barracks.  Furthermore,  they  were  living  much  more  in  the  open. 
It  was  found  that  in  commands  of  the  Service  of  Supply,  where  troops 
were  housed  in  barracks  with  a  large  number  of  men  to  a  single  room, 
the  epidemic  ran  much  the  same  course  with  high  mortality,  as  it  did 
in  the  cantonments  in  the  United  States.  The  percentage  of  infec- 
tion and  the  fatalities  from  influenza  and  pneumonia  in  France  were 
much  greater  among  troops  of  the  S.  O.  S.  than  among  troops  at  the 
front. 

Domestic  cleanliness. — We  have  studied  the  relationship  between 
influenza  incidence  and  the  cleanliness  of  the  household  by  the  same 
method  used  iti  studying  overcrowding.  In  Table  VIII  we  have  classi- 
fied according  to  cleanliness  and  according  to  the  number  of  cases  de- 
veloping in  each  family.  We  have  had  four  subdivisions,  ''very  clean," 
"clean,"  "dirty,"  and  "very  dirty."  There  is  greater  opportunity  for 
erroneous  results  in  this  table  than  in  the  one  preceding  because  the 
standards  of  cleanliness  are  difficult  to  define.  As  a  matter  of  fact  we 
are  guided  entirely  by  the  inspector's  own  impression  of  each  house- 
hold, as  she  examined  it  during  her  visits.  The  following  is  an 
excerpt  from  the  instructions  given  each  inspector  on  this  subject: 

"A  few  words  on  this  subject  may  describe  much.  State  of 
cleanliness  of  the  individual,  slovenly  condition,  dust  and 
dirt,  foulness  of  air  noticed  on  first  entering,  condition  of 
childrerL,  of  kitchen  sink,  etc.,  should  be  noticed,  and  good  or 
bad  features  recorded.  In  the  poorer  districts  not  a  few 
families  will  be  found  in  which  the  cleanliness,  considering  the 
surroundings,  is  quite  laudable.  Of  particular  importance 
are  amount  of  daylight,  ventilation,  care  of  bathroom  and 
toilet,  garbage,  whether  windows  are  kept  open  at  night." 

On  the  basis  of  these  returns  we  have  classified  the  famihes  as 
indicated,  but  each  inspector  was  governed  to  a  certain  extent  by  the 
average  cleanliness  of  her  district,  and  it  is  difficult  to  compare  the 
cleanest  tenement  with  any  of  the  districts  of  well-to-do  individuals. 
We  will  therefore  probably  find  it  more  profitable  and  more  nearly 


188 


INFLUENZA 


TABLE  VIII. 

Relationship  between  cleanliness  and  number  of  cases  in  family. 
(Clean  families  were  invaded  less  frequently  and  had  solitary  cases  more  often  than 

did  dirty  households.) 


Very  clean. 
(47.62  per  cent,  had  none.) 


Cases  in 
families. 

Total 
families. 

'18. 

Per  cent. 

•20. 

Per  cent. 

Both. 

Per  cent. 

Total. 

Per  cent. 

1 

124 

72 

15.65 

50 

10.87 

8 

1.74 

460 

26.96 

2 

53 

41 

8.91 

27 

5.87 

15 

3.25 

11.52 

3 

37 

33 

7.17 

13 

2.82 

9 

1.95 

8.04 

4 

18 

16 

3.48 

8 

1.74 

6 

1.30 

3.91 

5 

4 

3 

0.65 

2 

0.43 

1 

0.21 

0.87  [25.42 

6 

3 

3 

0.65 

0 

0.0 

0 

0.0 

0.65 

7 

2 

2 

0.43 

1 

0.21 

1 

0.21 

0.43  J 

8 

0 

0 

0 

0 

Clean. 
(41.52  per  cent,  had  none.) 


Cases. 

Families. 

'18. 

Per  cent. 

'20, 

Per  cent. 

Both. 

Per   cent. 

Total. 

Per  cent. 

1 

301 

212 

18.45 

120 

10.44 

31 

2.70 

1149 

26.19 

2 

177 

143 

12.45 

91 

7.92 

57 

4.96 

15.40 

3 

101 

83 

7.22 

52 

4.53 

34 

2.96 

8.79 

4 

52 

47 

4.09 

20 

1.74 

15 

1.26 

4.53 

5 

30 

29 

2.52 

17 

1.48 

16 

1.22 

2.61 

^ 32.29 

6 

8 

7 

0.61 

3 

0.26 

2 

0.17 

0.70 

7 

3 

3 

0.26 

0 

0.0 

0 

0.0 

0.26 

8 

0 

0 

0 

0 

Dirty. 
(36.89  per  cent,  had  none.) 


Cases  in 
faraUy. 

Total 
families. 

'18. 

Per  cent. 

'20. 

Per  cent. 

Both. 

Per  cent. 

Total. 

Per  cent. 

1 

79 

59 

17.40 

36 

10.62 

16 

4.72 

339 

23.30 

2 

58 

48 

14.16 

29 

8.55 

19 

5.61 

17.111 

3 

37 

31 

9.14 

22 

6.49 

17 

5.01 

10.91 

4 

26 

22 

6.49 

12 

3.54 

8 

2.36 

7.67 

5 

6 

5 

1.79 

4 

1.18    ■ 

3 

0.94 

1.77 

39.81 

6 

7 

7 

2.06 

4 

1.18 

4 

1.18 

2.06 

7 

0 

0 

0 

0 

8 

1 

0 

0.0 

1 

0.29 

0 

0.0 

0.29  J 

Very  dirty. 
(39.26  per  cent,  had  none.) 


1 

22 

16 

14.95 

8 

7.47 

2 

1.85 

107 

20.56 

2 

11 

8 

7.47 

6 

5.10 

3 

2.80 

10.28 

3 

14 

12 

11.21 

10 

9.35 

7 

6.54 

13.08 

4 

7 

5 

4.67 

4 

3.73 

2 

1.85 

6.54 

5 

6 

6 

5.10 

1 

0.93 

0 

0.0 

5.61 

40.18 

6 

3 

3 

2.80 

2 

1.85 

2 

1.85 

2.80 

7 

2 

2 

1.85 

0 

«0.0 

0 

0.0 

1.87 

8 

0 

0 

0 

0 

AN    KI'IDKMIOLOGIC    STUDY  189 

accurate  to  coniljinc  the  fjiioups  and  classify  thorn  only  as  "clean"  and 
•'dirty." 

But  even  without  combining  in  this  way,  the  tal>le  shows  us  that 
for  l)Oth  years  27  per  cent,  of  the  very  clean  families,  26  per  cent,  of  the 
clean,  23  per  cent,  of  the  dirty  and  21  per  cent,  of  the  very  dirty, 
had  but  one  case,  while  25  per  cent,  of  the  very  clean,  32  per  cent,  of  the 
dean,  40  per  cent,  of  the  dirty,  and  40  per  cent,  of  the  ver>'  dirty, 
had  multiple  cases. 

The  cleaner  the  family  the  less  is  the  likelihood  of  multiple  cases. 

It  is  rather  difficult  to  find  concrete  examples  of  the  influence  of 
domestic  habits  and  environment  in  the  1918  pandemic.  The  remark- 
ably high  incidence  among  the  natives  of  India  and  among  the  Ameri- 
can Indians  might  by  some  be  attributed  to  unfavorable  environment. 
Lynch  and  Gumming  obtained  records  from  a  large  number  of  insti- 
tutions and  from  business  concerns  having  their  own  records,  and 
discovered  that  the  influenza  incidence  was  higher  in  those  institu- 
tions where  dish  washing  was  done  manually  than  in  those  in  which 
mechanical  washing  was  performed.  They  appear  to  conclude  that 
the  difference  in  the  two  methods  of  washing  dishes  was  the  cause  for 
the  greater  incidence  in  influenza,  thus  bearing  out  their  theory  of 
the  propagation  of  influenza  chieflj^  through  eating  utensils.  On  the 
contrary  it  is  possible  that  the  presence  of  the  mechanical  washer  is  an 
indication  of  advanced  methods,  greater  care  in  the  kitchen,  and 
better  hygiene  probably  not  only  in  the  kitchen  and  dining  room,  but 
throughout  the  institution. 

Economic  status. — Although  in  our  survey  information  has  been 
obtained  regarding  the  economic  status  of  the  various  families  we 
would  not  stress  this  phase  of -our  subject.  Obviously  the  amount  of 
money  an  individual  has  in  his  bank  will  not  directly  influence  the 
amount  of  influenza  he  will  have  in  his  home.  As  nearly  an  accurate 
classification  by  wealth  is  by  the  separation  into  the  districts,  Districts 
I  and  III  being  very  poor.  District  II  poor.  Districts  IV  and  V  mod- 
erate, and  VI  well-to-do.  From  Chart  XXVI  we  see  no  definite 
relationship  between  influenza  incidence  and  economic  status. 

Dr.  Xiven  has  had  similar  experiences.  He  remarks  that  the 
disease  does  not  appear  to  have  affected  especiallj^  any  class  or  section 
of  the  community.  Rich  and  poor  suffered  alike.  Inquiry  in  some 
towns  shows  that  the  epidemic  not  infrequently  started  in  the  well- 
to-do  districts  and  only  later  involved  the  poorer  and  less  prosperous 
areas. 

We  cannot  state  with  any  degree  of  accuracy  in  what  section  of 


190  INFLUENZA 

Boston  the  1920  recurrence  first  began.  The  sections  studied  are  for 
relatively  small  portions  of  the  city,  and  it  is  possible  or  probable  that 
the  original  increase  was  in  some  area  outside  of  our  districts.  In  the 
districts  studied  the  earliest  increase  in  reported  cases  was  from  the 
section  of  the  city  known  as  Dorchester  (Districts  IV  and  V),  where 
there  was  some  increase  in  December,  1919.  The  latest  definite 
increase  was  in  the  Irish  district  of  South  Boston.  Geographically 
these  two  areas  are  quite  near.  The  relative  insusceptibility  of  the 
Irish  population  is  probably  a  much  more  important  factor  in  the 
difference. 

Frost  found  after  classifying  the  white  population  canvassed  in 
Little  Rock  and  San  Antonio  according  to  economic  status,  and  adjust- 
ing the  incidence  rate  in  each  group  to  a  uniform  sex  and  age  distri- 
bution, that  the  ratios  of  incidence  in  each  economic  group  to  incidence 
in  total  white  population  did  show  an  increase  with  increasing  poverty. 
"Notwithstanding  that  the  classification  according  to  economic  status 
is  a  very  loose  one,  based  solely  on  the  judgment  of  inspectors  with 
widely  different  standards,  a  considerably  higher  incidence  is  shown  in 
the  lower  as  compared  to  the  higher  economic  group." 

Parsons,  in  1891,  discussed  the  influence  of  poverty,  but  believed 
that  it  is  the  concomitants  of  poverty  which  were  the  cause  of  the 
higher  incidence  among  the  poor. 

"Sanitary  conditions  do  not  seem  to  have  had  any  influence  in 
determining  the  occurrence  of  influenza,  and  what  share  they  have  had 
in  determining  its  extent  or  fatality  cannot  yet  be  decided.  On  the 
occasion  of  the  last  great  epidemic.  Dr.  Peacock  concluded,  'The 
more  common  predisponents  to  disease,  e.  g.,  defective  drainage,  want 
of  cleanliness,  overcrowding,  impure  air,  deficient  clothing,  innutritions 
'  or  too  scanty  food,  powerfully  conduce  to  the  prevalence  and  fatality 
of  influenza.'  And  Dr.  Farr  showed  that  in  the  last  six  weeks  of 
1847,  while  in  the  least  unhealthy  districts  of  London  the  annual  rate 
of  mortality  was  raised  from  a  mean  rate  of  twenty  per  1,000  to 
thirty-eight,  in  the  unhealthiest  districts  it  was  raised  from  a  mean 
rate  of  twenty-seven  to  sixty-one. 

"That  overcrowding  and  impure  air  must  have  a  powerful  influ- 
ence in  aiding  the  development  of  the  epidemic  follows  from  what  we 
have  seen  of  its  greater  prevalence  among  persons  associated  together 
in  a  confined  space ;  and  though  rich  and  poor  have  alike  been  sufferers 
from  the  epidemic,  and  even  royal  personages  have  been  fatally 
attacked  by  it,  it  cannot  be  doubted  that  poverty  must  have  in  many 
'  cases  conduced  to  a  fatal  issue  in  persons,  who,  if  placed  under  more 


AN    EPIDEMIOLOGIC    STUDY  191 

favorable  circumstances,  might  have  recovered,  seeing  that  it  often 
involves  not  only  inferior  conditions  of  lodgment,  but  also  want  of 
appropriate  food,  of  sufficient  warmth  and  clothing,  and  of  ability  to 
take  the  needed  rest." 

Distribution  of  the  disease  through  the  household. — During  the 
autumn  and  winter  epidemic  of  1918  there  was  considerable  discussion, 
and  particularly  were  there  popular  newspaper  reports  of  entire 
families  being  taken  ill  with  influenza,  sometimes  all  on  the  same  day. 
This  was  less  true  of  1920.  But  few  of  us  are  personally  acquainted 
with  such  instances  and  at  best  they  must  have  been  relatively  rare. 

Among  1,236  families  with  influenza  in  either  epidemic  we  found 
only  94  or  7.6  per  cent,  in  which  the  entire  family  contracted  the 
disease.  No  family  consisting  of  over  seven  individuals  was  reported 
as  having  all  the  members  of  the  family  sick  in  either  epidemic.  Over 
two-thirds  of  the  families  with  even  numbers  of  individuals  (464  out  of 
605)  suffered  the  illness  of  less  than  half  of  the  household.  One 
quarter  of  all  families  of  more  than  one  (539  out  of  2,107)  had  but  one 
case  per  family.  Over  a  third  of  all  families  of  over  two  inividuals 
(745  out  of  2,006)  had  two  or  less  eases  per  household.  As  a  rule  there 
were  at  least  one  and  usually  several  individuals  in  each  household  who 
did  not  contract  influenza. 

That  as  a  rule  the  disease  did  not  appear  explosively  in  a  family; 
but  that  cases  developed  successively,  is  indicated  by  the  fact  that  out 
of  577  families  contracting  influenza  in  the  epidemic  of  1920  the 
cases  were  aU  of  simultaneous  development  in  but  fifteen.  In  thirteen 
of  these,  two  individuals  fell  ill  on  the  same  day  and  no  subsequent 
cases  developed.  In  the  other  two  families  three  individuals  came 
down  on  the  first  day  and  no  other  cases  developed.  In  addition  there 
were,  out  of  the  577  families,  fourteen  in  which  there  were  two  or  more 
cases  developing  on  the  first  day  of  the  invasion,  but  which  were  followed 
on  subsequent  days  by  later  cases  in  the  same  family.  Again,  there 
were  eleven  families  in  which  two  or  more  cases  occurred  simultane- 
ously at  an  interval  of  one  or  more  days  after  the  development  of  a 
single  prior  case. 

We  may  say  that  as  a  rule  in  the  1920  epidemic,  cases  of  influenza 
developed  in  families  successively  and  not  simultaneously.  In  only  29, 
or  5  per  cent,  of  the  families  contracting  the  disease  in  1920,  did  more 
than  one  case  develop  on  the  first  day  of  the  appearance  of  the  disease 
in  the  family. 

A  certain  difficulty  in  determining  the  date  of  onset  is  that  we 
must  rely  upon  the  patient 's  statement .     One  individual  may  have  been 


192  INFLUENZA 

sick  for  hours  or  days  before  a  second  member  coming  down  with  the 
disease  called  forth  recognition  of  the  fact  that  they  both  had  it. 

Unfortunately  we  are  not  able  to  give  similar  statistics  for  the 
1918-19  epidemic.  Our  investigation  occurred  so  long  after  the  epi- 
demic that  specific  dates  of  onset  of  the  disease  would  have  been 
entirely  unreliable.  The  nearest  date  we  have  attempted  to  obtain 
was  the  month  of  the  attack. 

Dr.  A.  L.  Mason  states  that  63  cases  came  under  his  observation  in 
the  epidemic  of  1889  as  occurring  in  groups  in  families.  In  but  six 
instances  were  two  persons  attacked  on  the  same  day.  The  average 
interval  between  cases  in  the  same  household  was  four  days.  Some- 
times a  week  or  more  elapsed.  Whole  families  were  never  stricken  at 
once. 

Parsons  in  1891  concluded  from  the  results  of  questionaires  sent 
to  physicians  that  in  the  first  spread,  1889-90,  there  was  an  interval 
between  cases  in  individual  households  just  as  we  have  described. 
Among  the  replies  to  his  questionaires  nine  described  intervals  of  one 
day  and  under,  six  described  intervals  of  two  days,  three  of  three  days, 
three  of  four  days,  and  four  replies  described  intervals  of  more  than 
four  days. 

Leichtenstern  observed  likewise:  "In  large  families  the  contagious 
character  of  influenza  is  evidenced  by  the  fact  that  the  other  members 
of  the  family  become  sick  one  after  the  other  following  the  first  case. 
This  rule  of  succession  is  most  easily  seen  in  the  early  or  late  period  of 
an  epidemic  and  is  less  noticeable  at  the  height,  where  the  opportunity 
for  all  the  members  of  the  family  to  acquire  the  infiuenza  outside  the 
home  is  enormous.  This  latter  fact  explains  why,  when  all  sicken  at 
once,  the  disease  appears  to  be  miasmatic  in  origin.  There  are  many 
examples  where  other  members  of  a  family  living  with  a  sick  individual 
remained  unaffected.  Parsons  reports  such  cases,  and  this  was  so 
frequently  the  case  that  some  British  physicians  state  that  it  is  the 
rule  that  there  is  but  one  case  in  a  family  or  that  the  cases  are  widelj^ 
separated  in  time.  This  was  only  partly  true  during  the  period  of 
the  pandemic  and  was  very  frequent  in  the  epidemic  following  it.  In 
this  respect  influenza  acts  like  the  common  contagious  diseases, 
diphtheria,  scarlet  fever,  measles,  etc.,  while  the  difference  lies  in 
the  short  incubation  period  and  the  very  high  contagiousness  of  the 
disease." 

That  West,  in  England,  had  observed  the  same  phenomenon  is  indi- 
cated by  the  following  quotation:  "How  is  it,  for  instance,  that  one 
member  of  a  household  may  be  picked  out  and  the  others  escape, 


AN    EPIDEMIOLOGIC    STUDY  193 

though  they  are  susceptible,  as  is  shown  by  their  acquiring  the  disease 
shortly  after  in  some  other  way?" 

Again  Leichtenstern  wrote:  "It  is  noteworthy  that  influenza  on 
ships  usually  did  not  occur  explosively,  but  spread  gradually,  and  on 
ships  usually  lasted  several  weeks,  as  on  the  Bellerophon,  from  the 
27th  of  March  to  the  30th  of  April;  on  the  Canada  from  the  11th  of 
April  to  the  24th  of  May;  on  the  Comus  from  the  10th  of  April  to  the 
3d  of  May. 

"The  German  Marine  Report  states,  'Everywhere  on  the  ships  the 
disease  began  not  suddenly  but  gradually.'  The  frigate  Schwalbe 
first  had  a  large  number  of  cases  only  on  the  6th  day  after  the  beginning 
of  the  epidemic.  There  are,  however,  some  exceptions,  where  the 
disease  has  begun  suddenly  with  the  greatest  violence  on  ships  as  on 
land.  Such  was  true  of  the  frigate  Stag  which  on  the  3d  of  April, 
1833,  neared  the  influenza  infected  coast  of  Devonshire,  and  as  it 
came  under  the  land  wind  the  epidemic  suddenly  broke  out  with 
great  violence.  Within  two  hours  forty  men  took  sick.  Within  six 
hours  the  number  had  increased  to  sixty.  Within  tw^enty-four  hours 
160  men  were  sick.  As  Parkes  has  remarked  the  evidence  is  insujfi- 
cient  that  there  had  been  no  communication  with  the  coast.  There 
have  been  other  examples  of  sudden  outbreaks  on  ships,  as  on  a  Dutch 
frigate  in  the  harbor  of  Mangkassar,  where  144  men  out  of  340  took 
sick  in  a  few  days  (1856);  on  the  Canopus  (1837)  in  the  harbor  of 
Plymouth,  where  on  the  15th  of  February  three-fourths  of  the  men 
took  sick  with  influenza." 

Garvie,  in  reporting  his  personal  experiences  with  influenza  in  1918 
in  an  industrial  area  in  England,  experiences  not  based  on  statistical 
study,  concludes  that  there  are  two  types  of  cases,  the  sporadic  case 
which  occurs  mainh^  among  the  wage-earning  members  of  the  family 
and  has  little  tendency  to  affect  other  members  of  the  household,  and 
second,  the  type  of  case  where  a  large  number  of  individuals  in  the 
household  are  affected.  He  called  this  the  "household  w^ave."  If 
we  interpret  him  aright  he  really  means  that  there  are  either  single 
or  multiple  cases,  and  that  the  single  cases  are  more  apt  to  occur  in  the 
wage-earner,  the  individual  who  is  more  exposed  on  the  outside  of  the 
household.  He  also  believes  that  the  household  wave  is  more  severe 
in  character  than  the  so-called  sporadic  case,  and  is  accompanied  by  a 
greater  number  of  complications. 

Armstrong,  in  his  survey  in  Framingham,  examined  influenza 
convalescents.  He  found  that  of  these  10  per  cent,  w^ere  in  families 
in  which  no  other  cases  had  developed,  and  87  per  cent,  were  in  families 


194  ^  INFLUENZA 

where  one  or  more  additional  cases  had  occurred.     In  three  per  cent, 
information  was  lacking. 

It  is  important  in  studying  the  literature  on  this  subject  to  dis- 
tinguish between  definitely  established  fact  and  less  definite  descrip- 
tion. Thus  one  is  still  left  in  some  doubt  when  one  reads  in  a  London 
letter  in  the  Journal  of  the  American  Medical  Association  for  1915 
concerning  the  epidemic  in  London  at  that  time  that,  ''whenever  it 
has  seized,  an  individual  it  has  usually  run  through  the  entire  house- 
hold.    Whole  offices  have  succumbed." 

The  first  case  in  the  family. — Chart  XXVII  shows  clearly  that  iu 
both  epidemics  in  our  experience  the  wage-earner  was  much  more 
frequently  the  first  case  in  a  family  than  was  any  other  occupation. 
The  individuals  whose  occupations  kept  them  at  home  were  second. 
Infants,  as  was  to  be  expected,  were  recorded  as  being  "first  case"  in 
the  smallest  number  of  instances. 

In  1889  the  distribution  was  practically  the  same.  Parsons  found 
that  out  of  125  households  the  first  case  was  a  bread-winner  in  96 ; 
a  housekeeper  in  nine;  a  child  at  school  in  thirteen;  a  child  not  at  school 
in  two  famihes.  In  the  last  five  famihes  the  first  case  was  in  adults, 
occupation  not  given.  This  order  is  identical  with  our  own.  Neither 
our  own  observations  nor  those  of  Parsons  consider  the  relative  pro- 
portions of  wage-earners  in  the  population  as  a  whole.  The  results 
are  nevertheless  suggestive. 

H.  F.  Vaughan  reached  comparable  results  for  the  1920  epidemic 
in  Detroit.  During  the  first  few  weeks  the  age  groups  from  20  to  29 
showed  a  relatively  much  more  frequent  influenza  incidence  than  did 
children  up  to  ten  years.  In  later  weeks  of  the  epidemic  there  was  a 
relative  increase  in  the  incidence  among  children  and  decrease  among 
young  adults.  He  concluded  that  the  disease  first  attacks  the  young 
adult  and  from  this  group  it  extends  into  the  home. 

In  the  Local  Government  Board  Report  for  1891,  H.  H.  Murphy 
distinguishes  three  groups  or  ways  in  which  the  disease  may  be  brought 
into  the  family.  The  examples  wiU  be  found  to  be  characteristic  for 
any  epidemic  and  for  any  country : 

Group  A. — Cases  of  single  exposure. 

"Household  1. — Mr.  Q.  goes  to  London  daily.  Was  ill  with  influ- 
enza on  December  25th.     No  other  case  in  this  house  tiU  January  15th. 

"Household  2. — Mrs.  A.  called  on  Mr.  Q.  on  December  31st,  and 
had  a  few  minutes'  conversation  with  him.  She  was  taken  ill  on 
January  3d.  There  was  a  Christmas  family  gathering  at  this  house, 
and  this  is  how  the  other  members  were  affected:  Mr.  B.,  January 


CHART  XXVII. 


Qccu  pa  - 

tlOHQ  1 

1 918-19 

19  20 

disf  ri  b- 
ut  ion 

■ 

of    fir-st 

1 

1 

1 

co^es   in 

1 

1 

1 

each  house- 
hold 

1 

1 

1 

1 

1 

Percent 

^8.9 

36.8 

II. 1 

252 

0.69 

39.8 

36.6 

142 

5.15 

4.1  Z 

Occu  bation 

1.^ 

1 

Ilk 
1^ 

0) 

1 

1 

^ 

■^ 

^ 

^ 

1 

16 


AN    EPIDEMIOLOGIC    STUDY  195 

6th;  Miss  C,  Mrs.  D.,  and  Master  D.,  January  8th;  Mr.  J.,  January 
10th;  Mr.  H.,  January  11th. 

''Household  3. — Miss  M.  went  to  a  party  January  3d.  She  had  a 
few  minutes'  conversation  with  a  young  lady  who  said  she  was  suffering 
from  influenza.  Miss  M.  had  a  characteristic  attack  on  the  6th  of 
January. 

"Household  4. — IMr.  G.  goes  to  London  daily;  taken  ill  January 
5th.  Mrs.  N.  visited  him  for  a  short  time  on  January  5th,  and  was 
taken  ill  Januarj'  10th." 

Group  B. — Where  disease  was  brought  from  a  distance  into  a 
previously  healthy  household. 

"Household  8. — Mrs.  R.  G.,  living  in  the  north  of  London,  came 
here  on  a  visit  December  17th.  On  the  19th  she  was  taken  ill  with 
influenza,  the  first  case  that  I  knew  of  in  this  neighborhood.  ]Mr. 
C.  G.,  on  the  23d,  servant  on  the  26th,  ]\Irs.  G.  31st,  and  Mr.  G. 
January  9th. 

"Household  9. — Mr.  I.  lives  at  his  business  place  in  London, 
taken  ill  December  20th  with  influenza.  His  family  reside  here. 
Boy  C.  visited  his  father  for  a  few  days,  and  came  back  ill  on  January 
4th.  The  other  members  of  the  family  were  attacked  as  follows: 
Baby,  8th;  Mrs.  and  boy,  12th;  boy,  18th,  girl,  22d;  girl  25th. 

"  Household  10. — Master  K.  stayed  a  few  days  with  some  friends  in 
London.  They  had  been  ill  with  influenza.  Returning  home  on 
December  31st  he  was  taken  ill.  Four  brothers  and  sisters  ill  on  the 
2d  January-,  !Mr.  K.  on  3d,  child  and  two  servants  on  the  5th,  Mrs.  K. 
on  the  7th." 

Group  C. — Where  the  source  of  infection  could  not  be  determined 
or  was  local. 

"Household  28. — Mrs.  D.  (who  thinks  she  got  it  shopping)  was 
taken  ill  2d  January,  her  daughter  on  the  5th,  and  Mr.  D.  on  6th. 

"Household  29. — Mrs.  L.  (who  thinks  she  got  it  shopping),  aged 
80,  had  influenza  badly  in  1847;  similar  symptoms,  but  much  milder, 
on  January  6,  1890;  Miss  L.  was  attacked  on  the  10th,  and  servant  on 
the  17th. 

Note. — A  former  attack  did  not  confer  immunity  after  forty-three 
years. 

"Household  30. — Mrs.  B.  (who  thinks  she  got  it  out  at  work) 
taken  ill  9th  January,  and  her  child  on  the  11th." 

In  ]\Iurphy's  complete  list,  one  of  the  most  frequent  remarks  is, 
Mr.  Blank  goes  to  London  daily.  Or,  Miss  Blank,  absent  on  a  visit, 
was  taken  ill  with  influenza  and  returned  home. 


196  INFLUENZA 

Again,  in  1890,  Dr.  Bruce  Low  studied  the  development  of  influ- 
enza at  East  Keal,  a  town  of  300  inhabitants.  We  quote  in  part  his 
description : 

"The  following  is  believed  to  have  been  the  commencement  of  the 
outbreak,  and  for  these  facts  I  am  indebted  to  Dr.  Francis  Walker, 
Medical  Officer  of  Health,  Spilsby,  R.  S.  D.  Mrs.  N.,  residing  at  East 
Keal  Hall,  went  to  London  (Forest  Hill)  on  a  visit  on  November  11th. 
She  visited  Barnum's  Show  on  November  13th.  She  became  ill  on 
the  night  of  the  14th.  Her  symptoms  were  those  of  a  cold,  attended 
with  sore  throat.  No  one  else  so  far  as  she  knew  was  ill  in  this  way  in 
the  house  before  her.  She  left  Forest  Hill  on  November  16th,  still 
feeling  very  unwell,  and  went  to  stay  with  friends  at  Kensington. 
She  was  too  ill  to  return  home  till  November  23d,  at  which  time  she 
was  still  feeling  very  weak.  She  heard  from  Forest  Hill  that,  directly 
after  she  left  one  of  the  inmates  of  the  house  where  she  had  been  visit- 
ing fell  ill  with  symptoms  similar  to  her  own.  Within  a  few  days, 
probably  about  the  27th  of  November  (the  exact  date  is  not  fixed), 
of  her  return  home,  her  son,  aged  four,  became  unwell  with  what 
appeared  to  be  an  ordinary  cold,  but  the  child  had  epistaxis;  he  soon 
recovered,  but  during  the  next  fortnight  the  four  servants  in  the  house 
were  ill  with  what  were  said  to  be  'colds,'  one  of  them  also  had  epistaxis. 
On  January  2d  another  son,  aged  six,  was  ill  with  'cold'  for  a  few  days; 
he  went  out  and  had  a  relapse,  which  compelled  him  to  stay  in  the 
house  for  another  week. 

"On  January  3d,  Mrs.  N.  again  fell  ill  with  'a  bad  cold,'  attended 
with  headache,  backache  and  epistaxis.  She  was  in  bed  two  days  and 
felt  miserable  and  prostrate  for  more  than  a  week  after.  On  January 
5th,  Mr.  N.,  her  husband,  had  headache,  backache,  and  general  sore- 
ness 'all  over.'  On  January  10th,  the  boy,  aged  four,  who  was  first 
attacked  after  his  mother's  return  from  London,  again  became  ill, 
his  symptoms  being  the  same  as  before.  The  only  other  remaining 
member  of  the  family  who  had  managed  to  escape  an  attack  of  'cold ' 
up  to  this  date,  was  said  to  have  felt  ill  the  day  the  boy  had  his  second 
attack;  but  the  illness  of  this  individual  was  slight,  and  only  caused 
suffering  for  one  night.  Thus  between  the  return  of  the  mother  on 
November  23d  and  January  10th  all  the  inmates  of  this  house,  nine 
in  number,  had  an  attack  of  illness,  evidently  of  the  same  nature.  A 
boy  who  works  in  Mr.  N.'s  yard  was  taken  ill  with  influenza  about  the 
end  of  November.  He  lives  in  the  village.  After  his  illness  his  four 
brothers  also  were  ill.  Dr.  Walker  says  that  'about  the  end  of  Nov- 
epaber'  cases  of  like  illness  were  beginning  to  crop  up  in  East  Keal. 


AN    EPIDEMIOLOGIC    STUDY  197 

Mrs.  W.,  the  wife  of  the  village  grocer  and  baker,  who  waited  on 
customers  in  the  shop  and  never  left  the  shop  or  house,  was  taken  ill 
on  the  afternoon  of  November  30th.  Next  morning,  December  1st, 
her  husband  and  six  children  were  all  attacked  in  the  same  way  with 
what  is  now  recognized  to  have  been  marked  influenza.  The  only- 
inmate  of  the  house  who  escaped  was  a  youth  employed  to  dcUver 
bread  and  groceries  in  a  cart  in  the  neighboring  village." 

Leichtenstern  relates  that  a  physician  traveling  from  Berlin  on 
the  10th  of  December  became  sick  in  his  home  town,  Elgesburg,  on 
the  8th  of  December,  but  he  made  several  visits  and  a  few  days  later 
those  people  seen  by  him  fell  sick,  while  otherwise  there  were  no  cases 
of  influenza  in  the  town  or  its  neighborhood.  These  cases  would 
probably  have  fallen  in  Group  C,  of  Murphy's  classification. 

Intimacy  of  family  contact. — We  have  been  able  to  discover  in  a 
representative  number  of  families  in  which  influenza  has  occurred, 
not  only  what  individuals  slept  in  the  various  rooms  of  the  household, 
but  also  what  individuals  slept  in  the  same  bed  with  influenza  cases. 
We  can,  therefore,  study  for  the  1920  epidemic  three  degrees  of  contact; 
contact  by  sleeping  with  a  case  of  influenza;  by  sleeping  in  the  same 
room  but  a  different  bed;  and  general  contact  by  being  in  the  family, 
but  sleeping  in  another  room.  For  brevity  we  designate  these, 
"sleeping,"  "room"  and  "family"  contact.  We  have  estabhshed 
similar  information  for  1918,  after  eliminating  families  in  which  deaths 
or  births  or  other  additions  or  losses  had  occurred  during  or  sub- 
sequent to  the  1918  pandemic,  in  which  there  has  been  a  change  of 
address,  in  which  the  cases  are  so  widely  separated  that  we  have 
designated  them  unrelated,  and  finally,  those  families  in  which  the 
information  has  been  insufficient.  With  the  remaining  we  have 
assumed  that  the  distribution  within  the  household  has  been  the  same 
in  both  epidemics.  Statistics  are  available  on  1,734  individuals  who 
in  1918  were  exposed  to  a  prior  case  in  the  family.  Of  these,  462 
developed  influenza  and  1,272  did  not.  26.6  per  cent,  of  exposed 
individuals  in  families  contracted  influenza,  without  respect  to  the 
degree  of  exposure. 


Intimacy  of  contact. 


Number  so  Number 

exposed.  infected. 


Per  cent, 
infected. 


"Sleeping". 
"Room"... 
"Family".. 


360 

303 

1,064 


166 

59 

273 


45.2 
19.5 
22.3 


45.2  per  cent,  of  individuals  sleeping  with  cases  of  influenza  in 
1918"  contracted  the  disease;  19.5  per  cent,  of  those  sleeping  in  the 


198 


INFLUENZA 


same  room,  but  different  beds  did  so;  22.3  per  cent,  of  those  living  in 
the  same  family,  but  sleeping  in  other  rooms  contracted  the  disease. 

Sleeping  contact  is  more  productive  of  influenza  than  are  the  less 
intimate  forms. 

Throughout  this  study  the  fact  that  there  are  multiple  possible 
sources  of  infection  both  outside  and  often  within  the  family  compli- 
cates the  picture. 

The  results  for  1920  are  similar.  Here,  30.0  per  cent,  of  all  indi- 
viduals sleeping  with  cases  of  influenza  contracted  the  disease,  17.7 
per  cent,  of  room  exposures  contracted  it,  while  but  11.5  per  cent,  of 
family  exposures  were  attacked. 

Four  hundred  and  sixty-three  or  29.1  per  cent,  of  the  total  of  2,193 
individuals  exposed  in  1920  had  had  the  disease  in  the  1918  pandemic. 
Did  they  show  by  reason  of  any  immunity  a  lower  attack  rate  for  the 
same  degree  of  exposure  than  other  individuals  in  1920? 


Type  of  exposure  in  1920. 

Per  cent,  of  exposed 

individuals  who  had  had 

influenza  in  1918-19 

and  who  contracted  it 

again;  per  cent. 

Per  cent,  of  those  who  had 
not  had  a  previous  attack, 
and  who  on  exposure  con- 
tracted influenza,  per  cent. 

"Sleeping" 

27.0 
18.3 
12.0 

31  0 

"Room" 

17  6 

''Family" 

11  2 

On  the  whole  there  is  no  evidence  of  protection  afforded  hy  a  previous 
attack. — Individuals  who  had  had  the  disease  before  succumbed  to  a 
second  attack  in  the  same  proportion  as  those  who  had  not  previously 
had  influenza. 

Recurrent  cases. — In  certain  families  there  were  individuals  who 
had  had  influenza  during  both  the  1918  and  1920  epidemics.  Were 
these  recurrent  cases  the  first  ones  to  occur  in  the  family,  or  did  they, 
as  a  rule,  follow  other  cases  in  the  same  household?  We  have  records 
of  236  recurrent  cases  in  which  we  know  the  order  of  occurrence  of  the 
various  cases  in  the  family.  Out  of  this  total  number  57  were  the 
initial  cases^in  the  household.  One  hundred  and  nineteen  were  the 
only  cases  occurring  in  the  family.  Therefore  176  or  74  per  cent,  of  the 
total  number  of  recurrent  cases  were  either  the  first  or  the  only  cases 
in  the  family.  Sixteen  recurrent  cases  followed  between  other  cases 
and  44  occurred  as  the  last  of  a  series  of  two  or  more  in  the  household. 


AN    EPIDEMIOLOGIC    STUDY  199 

SECTION  V. 
Immunity. 

Opinions  of  all  observers  who  have  studied  in  detail  the  question 
of  immunity  in  influenza  are  remarkedly  in  accord.  The  conclusions 
reached  by  Parkes  in  1876  are  valid  today,  and  form  as  excellent  an 
abstract  of  our  present  knowledge  as  any  produced  since  his  time. 
"There  is  some  discrepancy  of  evidence,  but,  on  the  whole,  it  seems 
clear  that,  while  persons  seldom  have  a  second  attack  in  the  same 
epidemic  (though  even  this  may  occur),  an  attack  in  one  does  not 
protect  against  a  subsequent  epidemic.  Indeed,  it  has  been  supposed 
rather  to  render  the  body  more  liable." 

In  1890,  Abbott  wrote:  "There  is  but  little  if  any  evidence  in 
support  of  the  protective  power  of  one  attack  to  confer  immunity  against 
a  second;  and  hence  adults  are  not  exempt,  as  they  usually  are  in 
epidemics  of  scarlet  fever  or  other  exanthemata;  so  that  the  propor- 
tion of  adults  to  children  attacked  in  an  epidemic  is  necessarily  greater 
than  that  which  is  observed  in  epidemics  of  other  infectious  diseases." 

Parsons  made  somewhat  similar  observations:  "One  attack  of 
influenza  does  not  seem  to  be  protective  against  another;  the  disease  in 
this  respect  resembling  diphtheria,  erysipelas,  and  cholera  rather  than 
small-pox,  measles,  or  whooping  cough.  The  duration  of  the  epidemic 
in  a  locality  is  so  short  that  it  is  dijficult  to  distinguish  between  second 
attacks  properly  so-called,  and  relapses,  which  are  frequent  enough. 
A  case  is  recorded  in  the  'British  Medical  Journal'  of  February  15,  1890, 
in  which  a  patient  who  had  suffered  from  influenza  in  France  in 
December,  1889,  had  another  attack  in  England  in  January,  1890. 
It  was  noticed  in  1837  that  many  persons  suffered  from  influenza 
who  had  had  the  disease  during  the  previous  epidemic  in  1834.  The 
shortness  of  the  interval  between  these  two  epidemics,  as  compared 
with  that  between  1848  and  1889,  seems  to  show  that  the  periodical 
return  of  the  disease  in  an  epidemic  form  does  not  depend  upon  the 
accumulation  in  the  interval  of  susceptible  individuals  unprotected 
against  the  disease  by  a  previous  attack.  If  one  attack  afforded  pro- 
tection against  another  a  large  proportion  of  the  population  in  1837 
must  have  been  protected,  yet  an  epidemic  occurred,  and  on  the  other 
hand  for  many  years  before  1889  a  large  majority  of  the  population 
must  have  been  unprotected  by  a  previous  attack,  yet  the  epidemic  did 
not  recur. 


200  INFLUENZA 

"The  persons  now  living  who  passed  through  the  disease  in  1847 
are  of  course  comparatively  few,  but  such  persons  have  not  been 
exempt  from  the  present  epidemic. 

' '  I  should  be  inclined  to  attribute  the  short  duration  of  the  influenza 
epidemic  in  a  locality  to  the  establishment  of  a  tolerance  for  the 
specific  poison  among  the  persons  exposed  to  it,  similar  to  the  tolerance 
for  dust  possessed  by  workmen  in  rag  factories,  as  mentioned,  but 
which  i»  soon  lost  on  their  ceasing  to  be  exposed  to  it,  rather  than 
to  a  true  immunity  being  established. 

"Relapses  in  influenza  are  of  frequent  occurrence;  they  occurred 
in  9.2  per  cent,  of  the  cases  at  the  Morningside  Asylum,  Edinburgh, 
and  in  some  cases  indeed  a  second  relapse  has  been  recorded.  The  time 
at  which  the  relapse  occurs  is  usually  from  a  week  to  a  fortnight  after 
the  primary  attack,  and  it  can  often  be  distinctly  traced  to  an  exposure 
to  cold,  or  return  to  work  before  complete  recovery.  The  symptoms 
of  the  relapse  are  similar  to  those  of  the  primary  attack,  except  that 
they  are  commonly  more  severe." 

In  his  report  of  1893,  Parsons  goes  into  the  subject  of  recurrent 
attacks  in  individuals  in  greater  detail.  He  quotes  several  com- 
munications received  from  various  physicians  and  health  officers. 
These  opinions  differ,  some  believing  that  the  disease  predisposes  to 
another  attack;  others,  that  there  is  no  effect  on  the  incidence  in 
recurring  epidemics;  and  still  others  believing  that  there  is  a  small 
amount  of  acquired  immunity.  The  communications  are  not  based 
upon  statistical  evidence.  He  does  find,  however,  an  opportunity 
for  statistical  study  in  the  industrial  schools  at  Swinton  near  Man- 
chester: "These  schools  were  severely  affected  in  March,  1890,  171 
out  of  589  children  having  suffered,  or  29  per  cent.  In  the  first  epi- 
demic of  1891  they  were  again  affected,  but  to  a  less  extent,  only  35 
cases  occurring.  At  that  time  there  were  in  the  schools  449  children 
who  had  been  there  at  the  time  of  the  former  epidemic.  Of  these 
150  had  had  influenza  in  1890  and  4  of  them  had  it  again,  or  2.6  per 
cent.;  299  had  escaped  influenza  in  1890  and  17  of  these  had  it  now,  or 
5.7  per  cent.  Thus,  so  far  as  these  figures  go,  an  attack  of  influenza 
confers  a  degree  of  protection  which  after  the  lapse  of  a  year  diminishes 
by  one  half  the  liability  to  contract  the  disease." 

Leichtenstern,  like  Parsons,  recognizes  the  importance  of  distin- 
guishing between  relapses  and  recurrent  cases.  Relapses  in  influenza 
are  not  common.  They  usually  occur  after  the  patient  is  up,  and 
about  when  he  is  ready  to  leave  the  house.  These  are  not  recurrent 
cases,  but  in  the  epidemics  in  the  years  following  1889  there  were 


AN    EPIDEMIOLOGIC    STUDY  201 

plenty  of  well  substantiated  cases  of  recurrent  typical  influenza  in  the 
same  individual  and  some  times  even  in  entire  families.  During  the 
1889  epidemic,  as  during  the  1918  epidemic  it  has  been  suggested  by 
various  observers  that  the  apparent  immunity  among  the  very  old 
was  due  to  immunity  developed  as  the  result  of  previous  epidemics, 
such  as  that  of  1837,  1847  and  1857.  Leichtenstern  has  collected  the 
statistics  from  five  different  hospitals  in  which  8,  32,  35,  24,  and  24 
per  cent,  of  individuals  attacked  in  1891-92  had  already  had  the 
disease  in  1889. 

AUbutt  in  1905  remarked  that  whereas  he  had  previously  believed 
that  immunity  to  influenza  usually  persists  as  long  as  six  months, 
many  cases  had  recently  been  brought  to  his  notice  where  such  an 
interval  seemed  improbable,  where  the  succeeding  attack  was  probably 
not  a  relapse  but  a  new  infection.  He  has  seen  two  attacks  apparently 
separate  occurring  in  the  same  individual  within  two  months.  In 
the  same  year  Moore  wrote  that  influenza  shows  a  decided  tendency 
to  relapse,  a  feature  to  which  the  indirect  fatality  of  the  disease  is  in 
great  measure  due.  "So  far  from  establishing  immunity,  an  attack 
of  this  malady  seems  to  render  an  individual  more  liable  to  contract 
the  disease  upon  any  future  exposure  to  its  contagion." 

Again  West,  in  the  same  year  wrote,  "From  our  present  experience 
we  must  conclude  that  influenza  is  infectious  in  a  very  high  degree 
indeed,  and  that  the  protection  afforded  by  an  attack  is  imperfect, 
or  of  very  short  duration.  Indeed,  one  attack  seems  actually  to 
predispose,  after  a  time  to  another,  or,  to  put  it  differently,  that  the 
positive  phase  of  protection  is  followed  by  a  negative  phase,  in  which 
the  individual  seems  rather  more  than  less  liable  to  succumb  to  infec- 
tion if  exposed  to  it.  It  seems  more  likely  that  an  individual  may 
never  have  influenza  at  all  than  that,  having  had  it  once,  he  should 
never  have  it  again.  Some,  indeed,  seem  to  offer  so  Httle  resistance 
that  they  develop  it  regularly  once  or  twice  a  year." 

We  have  previously  shown  that  the  relatively  low  morbidity  among 
the  older  age  groups  in  1918  is  not  satisfactorily  explained  by  an 
immunity  lasting  over  from  the  epidemic  of  1889-93.  If  such  were  the 
case  the  change  in  mortality  rate  in  large  groups  of  individuals  would 
occur  at  the  age  of  30. 

During  the  autumn  of  1918  many  observations  were  made,  particu- 
larly in  the  armies,  of  light  incidence  in  those  groups  or  communities 
that  had  had  the  disease  in  mild  form  in  the  spring  of  the  same  year. 

Parsons  quotes  many  similar  observations  for  the  period  1890-1893. 

V.  C.  Vaughan  relates  that  at  Camp  Shelby,  Mississippi,  "there 


202  INFLUENZA 

was  in  April  a  division  of  troops  numbering  about  26,000.  An  epi- 
demic of  mild  influenza  struck  this  camp  in  April,  1918,  and  within 
ten  days  there  were  about  2,000  cases.  This  included  not  only  those 
who  were  sent  to  the  hospitals,  but  also  those  who  were  cared  for  in 
barracks. 

This  was  the  only  division  that  remained  in  this  country  without 
change  of  station  from  April  until  the  fall  of  1918. 

"During  the  summer  this  camp  received  20,000  recruits.  In 
October,  1918,  the  virulent  form  of  influenza  struck  this  camp.  It 
confined  itself  almost  exclusively  to  the  recruits  of  the  summer  and 
scarcely  touched  the  men  who  had  Uved  through  the  epidemic  of 
April.  Not  only  the  2,000  who  had  the  disease  in  April,  but  the  24,000 
who  apparently  were  not  affected  escaped  the  fall  epidemic.  It 
appears  from  this  that  the  mild  form  of  influenza  of  April  gave  a 
marked  degree  of  immunity  against  the  virulent  form  in  October. 
There  is  another  observation  which  points  the  same  way.  Looking 
over  the  statistics  of  the  fall  epidemic  in  cities  in  the  United  States  we 
find  that  certain  cities  had  a  low  death  rate,  while  others  had  a  rela- 
tively high  rate.  Among  those  cities  which  had  a  low  death  rate  we  will 
mention  Atlanta,  Ga.;  Kansas  City,  Mo.;  Detroit,  Mich.,  and  Colum- 
bus, Ohio.  Going  to  the  spring  records  of  these  cities  we  find  that  in 
all  of  them  in  March  and  April  of  1918  there  was  an  unusually  high 
death  rate  from  pneumonia  and  undoubtedly  in  these  cities  at  that 
time  there  was  a  relatively  mild  epidemic  of  influenza.  In  this  way  I 
am  inclined  to  account  for  the  relatively  low  death  rate  in  these  cities 
in  the  fall  of  1918.  I  make  no  claim  that  this  and  other  instances  of  a 
similar  kind  prove  that  the  mild  and  virulent  forms  of  influenza  are 
manifestations  of  the  same  disease,  but  I  do  hold  that  the  evidence 
points  that  way." 

Lemierre  and  Raymond  report  the  following  observation  in  favor 
of  the  development  of  a  certain  degree  of  immunity  in  the  French 
troops  in  April,  1918.  After  an  intervening  period  of  quiescence 
there  was  a  manifest  recrudescence  at  the  end  of  August.  Many 
military  formations  were  attacked  during  both  periods.  This  was 
true  especially  in  three  groups  of  an  artillery  regiment  under  their 
observation.  In  the  first  of  these  groups  there  were  three  cases  in 
April,  while  114  men  were  attacked  in  August.  In  the  third  group 
there  were  100  cases  in  April  and  only  3  in  August.  In  the  second 
group  there  were  20  cases  in  April  and  59  in  August.  Their  report 
does  not  state  the  total  number  of  individuals  in  each  of  the  three 
groups. 


AN    EPIDEMIOLOGIC    STUDY  203 

Joltrain  and  Baufle  discuss  the  flaring  up  of  the  epidemic  in  Octo- 
ber, and  relate  that  a  troop  of  soldiers  from  Indo-China  nearly  all  had 
the  disease  lightly  in  the  spring,  but  when  the  disease  appeared  again 
it  spared  this  troop  completely,  while  troops  and  civilians  around 
developed  it  in  a  severe  form. 

Gibbon  writes:  " During  the  last  three  waves  of  the  epidemic  I  had 
to  deal  with  the  sick  of  2,000  troops,  and  during  this  time  we  treated 
in  hospital  over  400  cases.  No  cases  admitted  in  June,  July  or  August 
were  re-admitted  in  October,  November,  or  December,  and  no  cases 
admitted  in  either  of  these  two  periods  were  re-admitted  in  February 
this  year.  Unfortunately  I  am  unable  to  trace  the  cases  into  March 
as  the  troops  were  changed." 

Dopter  reports  recurrent  epidemics  of  influenza  in  a  French  Army 
Division  in  1918.  The  division,  of  which  he  was  surgeon,  was  one  of 
the  first  to  contract  la  grippe  at  the  time  of  its  first  appearance  in  the 
zone  of  the  armies  at  the  end  of  April,  1918.  At  this  time  nearly  the 
entire  body  of  infantry  troops  was  attacked.  The  disease  was  mild, 
and  without  compHcations.  The  regiment  of  artillery  escaped  nearly 
entirely.  This  epidemic  subsided  very  rapidly,  and  by  the  end  of  May 
it  had  entirely  disappeared.  Early  in  August  a  group  of  heavy  artil- 
lery was  attached  to  the  division,  bringing  influenza  with  it.  Then  a 
few  cases  appeared  in  the  regiment  of  hght  artillery  which  had  hitherto 
escaped.  By  the  end  of  August  all  three  groups  of  this  regiment  had 
been  attacked.  In  this  second  epidemic  the  men  who  had  come 
through  the  first  unattacked  were  very  severely  ill  in  the  second. 

With  rare  exceptions  those  sick  in  the  first  did  not  contract  it 
again.  Dopter  notes  that  in  the  battery  the  most  severely  affected 
in  August,  of  which  the  effectives  were  reduced  almost  to  none,  only 
those  men  were  considered  well  enough  for  duty  who  had  had  influ- 
enza in  the  first  period.  They  escaped  the  second  in  spite  of  the  close 
contact  with  their  comrades.  The  infantry  regiments,  which  were  in 
close  association  with  the  artillery,  remained  unaffected. 

Finally,  toward  the  middle  of  September  new  troops  were  attached 
to  the  division,  in  view  of  an  imminent  attack  by  the  enemy.  These 
troops,  coming  from  neighboring  and  distant  formations  were  suffering 
at  the  time  from  grip,  and  continued  to  have  the  disease  in  the  new 
sector.  Again,  those  attacked  in  May  passed  without  damage  through 
this  new  epidemic.  Among  them  there  were  only  rare  isolated  mild 
cases.     The  recurrences  made  only  1.6  per  cent,  of  the  total  incidence. 

Opie  and  his  associates  found  that  at  Camp  Funston  after  the  first 
wave  of  influenza  in  March  and  April,  1918,  the  succeeding  waves 


204  INFLUENZA 

usually  affected  only  new  recruits,  who  had  not  been  in  camp  during 
previous  waves. 

In  Calcutta  influenza  appeared  as  an  epidemic  in  July,  1918,  and 
in  November,  1918.  During  the  first  quarter  of  1919,  at  Calcutta  as 
elsewhere,  many  cases  were  still  recurring.  Malone  investigated  the 
incidence  of  the  disease  in  three  institutions  of  Calcutta :  He  found  that 
in  the  Gourepore  Jute  Mills  where  the  population  was  practically 
stationary,  those  individuals  who  were  attacked  in  July,  1918,  passed 
through  two  later  epidemics,  in  December,  1918,  and  February,  1919, 
without  contracting  the  disease  a  second  time,  in  spite  of  intimate 
contact  with  infected  persons.  The  same  was  true  according  to 
Malone  in  the  Alipore  Central  Jail  and  the  Presidency  Jail  in  Calcutta. 
He  believes  that  his  evidence  strongly  suggests  an  immunity  lasting 
for  at  least  nine  months. 

Dunlop  found  that  Glasgow  had  a  mild  epidemic  in  the  month  of 
May,  1918,  in  which  the  death  rate  rose  from  14.1  to  20.1.  There  is 
no  record  of  any  similar  outbreak  in  Edinburgh.  In  the  July  epidemic 
the  Glasgow  death  rate  rose  from  11.7  to  15.9,  while  the  Edinburgh 
death  rate  went  from  11.3  to  18.0,  a  higher  increase.  In  the  October- 
November  epidemic  the  Glasgow  rate  rose  from  11.0  to  38.4,  while  the 
Edinburgh  rate  went  from  10.8  to  46.2.  In  the  February-March 
epidemic  the  Glasgow  rate  rose  from  14.9  to  48.3,  and  the  Edinburgh 
rate  from  18.9  to  52.1  In  the  July  and  October  epidemics  Edinburgh 
showed  a  greater  increase  in  death  rate,  while  in  February,  1919, 
the  increase  in  the  two  cities  was  the  same.  However,  in  this  case 
probably  other  factors  play  a  part.  Also,  we  must  remember  that 
here  we  are  dealing  with  death  rates,  not  with  incidence  rates. 

The  Inspector  General  of  Health,  in  Spain,  reported  in  January, 
1918,  that  those  cities  which  had  the  disease  in  May,  1918,  suffered 
lightly  in  the  autumn  of  that  year,  while  others  of  the  large  cities 
which  had  been  spared  in  the  first  invasion  suffered  most  in  the  second. 

Maillard  and  Brune  report  an  epidemic  of  influenza  in  an  epileptic 
colony.  There  were  32  deaths  among  the  63  cases.  None  of  the 
inmates  of  the  hospital  who  had  influenza  during  the  June  epidemic 
contracted  it  anew  during  the  October  wave. 

Ovazza  records  that  although  a  number  of  persons  contracted 
the  influenza  anew  on  its  return  in  the  fall  after  having  had  it  in  the 
spring,  yet  the  return  cases  were  strikingly  mild,  and  always  free  from 
complications. 

Barthelemy  describes  the  successive  waves  of  epidemic  influenza 
at  Bizerte.     He  found  that  the  doctors  and  nurses  who  had  been 


AN    EPIDEMIOLOGIC    STUDY  205 

through  the  first  epidemic  did  not  develop  influenza  in  the  second  one 
a  few  months  later,  even  though  they  came  in  the  closest  contact  with 
the  patients. 

Hamilton  and  Leonard  have  studied  two  successive  outbreaks  due 
to  lapses  in  a  rigid  quarantine  in  an  institution  of  180  girls  between  12 
and  18  years  of  age.  The  girls  were  distributed  through  six  cottages. 
In  the  first  epidemic  November,  1918,  76  girls  contracted  the  disease, 
at  which  time  it  was  entirely  limited  to  the  occupants  of  cottages  2,  3, 
and  4.  The  second  outbreak  occurred  in  January,  1919,  when  82 
took  ill.  Only  five  of  these  were  located  in  cottages  2  and  4,  the  re- 
mainder being  in  1,  5  and  6.  No  cases  occurred  in  cottage  3  during 
the  second  spread.  Both  epidemics  lasted  a  little  under  two  weeks. 
Those  who  had  suffered  in  the  first  spread  appeared  to  be  immune  to 
the  second.  There  were  no  recurrences.  The  second  epidemic  was 
much  milder  in  character.  Twelve  per  cent,  of  the  total  remained 
well  throughout  both  epidemics. 

Dr.  Niven,  in  his  study  of  1,021  households  previously  described, 
found  that  105  families  suffered  in  both  the  summer  and  autumn  1918 
epidemics.  "They  comprised  a  population  of  565  persons,  of  whom 
205  suffered  in  summer  and  360  escaped.  In  the  autumn  epidemic 
eighty-two  (or  40  per  cent.)  of  the  presumably  'protected'  persons 
succumbed  again,  whereas  only  120  (or  33  per  cent.)  of  the  'unpro- 
tected' suffered.  Of  the  former,  however,  only  one  died,  while  five 
of  the  latter  terminated  fatally.  These  are  interesting  figures.  If 
they  are  borne  out  by  subsequent  inquiry,  they  are  somewhat  difficult 
of  explanation.  The  persistent  susceptibility  to  the  primary  disease 
and  yet  comparative  immunity  from  the  fatal  sequel,  would  seem  to 
suggest  a  dual  infection,  against  one  element  of  which  the  body  is  able 
to  produce  protection,  while  it  is  unable  to  do  so  against  the  other." 

Frost  made  a  canvass  of  33,776  individuals  in  Baltimore  between 
November  20th  and  December  11th,  1918.  The  same  population  was 
again  covered  in  January,  1919,  to  determine  the  extent  of  the  recru- 
descence reported  in  December.  Among  32,600  people,  724  cases  of 
influenza  had  occurred  in  the  interval  since  the  first  survey.  Of  this 
number  only  26  or  3.6  per  cent,  were  definitely  cases  of  second  attack 
in  the  same  individual.  Even  in  these  cases  the  diagnosis  is  necessarily 
uncertain.  Frost  says  that  considering  that  23  per  cent,  of  the  popula- 
tion had  had  influenza  prior  to  December  11th,  the  proportion  of 
second  attacks  should  have  been  much  greater  if  no  immunity  had 
been  acquired.  A  second  canvas  in  San  Francisco  gave  generally 
corresponding  results. 


206  INFLUENZA 

Our  own  experience  was  quite  similar.  We  have  divided  the  whole 
period  from  March,  1918  to  March,  1920,  into  two  portions  separated 
at  August  1,  1919.  In  the  first  portion  we  have  knowledge  of  but  four 
individuals  suffering  from  what  the  records  would  indicate  to  be  two 
genuine  attacks  of  influenza.  Similarly,  five  individuals  appeared  to 
have  had  two  attacks  within  the  second  interval.  These  are  to  be 
contrasted  with  a  total  incidence  in  the  fall  and  winter  of  1918-1919 
of  1,971  cases,  and  in  the  winter  of  1919-20,  of  965  cases.  Among  the 
total  nine  individuals  the  intervals  between  attacks  varied  from  26 
days  to  five  months.  All  except  one  had  an  interval  of  one  month  or 
over.  In  two  cases  there  was  an  interval  of  one  month,  in  one  an 
interval  of  two  months,  in  two  an  interval  of  three  months,  in  one  of 
four  months,  and  in  one  of  five  months.  None  of  the  four  individuals 
who  had  two  attacks  in  the  first  group  of  months  had  a  subsequent 
attack  in  the  second.  On  the  contrary,  two  of  the  five  suffering  two 
attacks  in  the  second  group  of  months  had  one  previous  attack  in  the 
first.  The  second  attack,  following  the  first  by  a  relatively  short 
interval  tended  to  be  milder  than  the  first.  In  five  out  of  the  entire 
nine  the  second  attack  was  milder,  in  two  it  was  of  the  same  degree 
of  severity,  and  in  only  two  was  it  more  severe  than  the  first.  The 
order  of  severity  in  the  two  individuals  having  three  attacks  each 
was,  in  the  first,  severe,  mild,  severe;  in  the  second,  severe,  average, 
average. 

Zinsser  makes  the  following  remark:  "The  writer  himself  believes 
that  he  had  three  attacks  during  the  last  epidemic.  The  first  and 
second  were  mild  ones  and  the  third  complicated  and  therefore  severe ; 
and  innumerable  others  with  whom  he  has  spoken  have  had  similar 
experiences." 

From  a  consideration  of  these  reports  by  divers  authorities  it  is 
reasonable  to  conclude  that  for  a  period  of  a  few  months  at  least,  one 
attack  of  influenza  protects  against  a  second.  As  is  to  be  expected, 
this  relative  immunity  is  not  of  constant  duration  in  all  individuals. 
If  there  were  no  lessened  susceptibility  following  an  attack  we  would  be 
faced  with  the  phenomenon  of  individuals  succumbing  time  and  again 
to  rapidly  successsive  attacks  of  the  disease.  Such  a  circumstance  is 
very  rare. 

It  is  difficult  to  determine  how  long  even  on  an  average  this  relative 
protection  or  insusceptibility  lasts.  Evidence  is  fairly  uniform  in 
indicating  a  protection  of  at  least  three  months.  Usually  it  is  longer. 
There  seems  to  be  some  basis  for  the  supposition  that  a  group  of  indi- 
viduals exposed  to  an  attack  of  influenza  displays  within  the  succeed- 


AN    EPIDEMIOLOGIC    STUDY  207 

ing  three  months,  or  shghtly  longer,  a  relative  general  group  immunity. 
If  the  group  be  considered  as  a  whole  those  even  who  did  not  develop 
the  disease  previously  appear  to  have  become  less  susceptible. 
Whether  we  can  ascribe  this  to  the  iiulividual  as  a  unit,  or  whether  we 
must  explain  it  by  some  assumption  with  the  community  as  a  unit, 
is  uncertain.  Is  it  because  the  exposed  individuals  in  the  group  who 
did  not  contract  the  disease  have  individually  received  some  of  the 
virus  into  their  systems  and  developed  a  certain  immunity,  or  is  it  a 
much  more  complex  phenomenon  depending  on  greater  relative  dis- 
persion of  susceptibles  and  other  communal  factors? 

We  may  place  the  minumum  period  of  "immunity  "  at  from  three  to 
five  months,  rarely  less.  There  is  additional  evidence  by  which  we  may 
delimit  fairly  closely  the'other  extreme,  that  time  at  which  individuals 
considered  as  a  group  no  longer  manifest  increased  resistance  to  the 
disease. 

The  author  found  that  19.17  per  cent,  of  his  populaticwi  contracted 
influenza  in  1918,  and  9.55  per  cent,  contracted  the  disease  in  1920. 
Two  hundred  and  forty  individuals,  or  2.4  per  cent,  of  the  entire 
population  developed  the  disease  in  both  epidemics.  Out  of  1,97] 
individuals  having  the  disease  in  the  1918  spread,  240,  or  12.1  per 
cent,  recurred  in  1920.  This  is  to  be  compared  with  the  total  1920 
incidence  of  9.55  per  cent.  More  correctly  we  should  separate  the 
1920  cases  into  two  groups,  those  who  had  and  who  had  not  had 
influenza  previously.  The  former  group,  240  indi\'iduals,  constitute 
as  just  stated,  12.1  per  cent,  of  all  who  had  had  the  disease  previously. 
The  second  group,  715  individuals,  constitute  8.9  per  cent,  of  the 
8,034  who  had  not  had  the  disease  in  1918-19. 

From  these  results  we  must  conclude  that  a  previous  attack  con- 
tracted on  an  average  of  from  10  to  17  months  before,  conferred  no  pro- 
tection whatever  against  a  second  attack.  On  the  contrary,  the  attack 
rate  was  slightly  higher  in  this  group  than  in  those  who  had  not  previously 
had  the  disease. 

Yet  another  evidence  of  the  insignificant  part  played  b}^  any  immu- 
nity in  the  occurrence  of  influenza  in  individuals  in  1920  is  indicated  by 
our  series  of  319  infants  living  in  1920  but  who  had  not  been  born  dur- 
ing the  1918  spread  and  who  were  presumably  not  immune  to  the 
disease.  We  have  not  investigated  whether  the  mothers  had  had  the 
disease  in  1918.  From  among  these  319  infants,  thirty  or  10  per  cent., 
developed  the  disease  in  1920.  This  is  practically  the  same  percentage 
as  for  the  population  at  large. 


208 


INFLUENZA 


These  findings  also  correspond  with  our  previously  recorded  con- 
clusion made  after  studying  the  disease  incidence  with  three  increasing 
degrees  of  exposure,  sleep,  room  and  family  (page  198). 


TABLE  IX. 

Comparison  of  the  severity  of  the  first  and  second  attacks  in  individuals  contracting 
influenza  in  1918-19  and  again  in  1920. 


Severity. 

No.  of  cases. 

Comparison. 

No.  of  cases. 

1918-19. 

1920. 

Average 

Severe 

Severe 

Mild 

Mild 
Average 

43 
50 
39 

Second  attack 
milder 

132 

Mild 

Average 

Severe 

Mild 
Average 

Severe 

30 
22 
20 

Both  of  equal 
severity 

72 

Mild 
Mild 
Average 

Average 

Severe 

Severe 

13 
5 

18 

Second  more 
severe 

36 

Altho  we  find  no  conclusive  evidence  of  protection  against  recur 
rent  attacks,  we  do  find  (Table  IX)  that  the  second  attack  in  the  same 
individual  was  usually  milder.  However,  the  1920  epidemic  as  a 
whole  was  milder,  (Chart  XVIII) . 

Zinsser  quotes  a  letter  from  Frost  in  which  the  latter  states  that 
in  Baltimore  those  persons  who  were  attacked  during  the  1918-19 
epidemic  showed  no  relative  immunity  during  the  epidemic  of  1920. 
This  is  not  a  contradiction  to  the  earHer  Baltimore  studies,  since  in  that 
case  the  interval  between  the  epidemic  waves  was  not  more  than  about 
three  months. 

Jordan  and  Sharp  have  obtained  statistics  regarding  approxi- 
mately 4,000  men  at  the  Great  Lakes  Naval  Training  Station.  The 
men's  statement  regarding  previous  influenza  was  accepted  whenever 
the  attack  was  said  to  have  occurred  during  the  influenza  period  of 
1918-1919,  i.e.,  in  September,  October,  November,  December,  January, 
February  and  March.  The  great  majority  were  reported  for  the  period 
of  September  to  December.  Only  a  few  cases  were  reported  as  oc- 
curring in  March,  and  perhaps  these  actually  occurred  somewhat  earlier 
than  the  men  recalled.  A  few  cases  were  accepted  as  influenza  when 
reported  as  occurring  in  Europe  during  July  and  August,  1918. 

They  found  that  28.5  per  cent,  of  3,905  men  had  had  the  disease  in 


AN    EPIDEMIOLOGIC    STUDY  209 

1918,  and  that  22.6  per  cent,  were  attacked  in  1920.  Of  those  who  had 
the  disease  in  1918-19,  21.2  per  cent,  had  a  repeated  attack  in  1920, 
while  of  those  who  had  not  had  a  previous  attack,  23.1  per  cent,  were 
attacked  in  1920. 

A  similar  study  among  2,472  men  at  Camp  Grant  showed  that  15.8 
per  cent,  had  had  influenza  in  1918-19,  and  11.7  per  cent,  in  1920.  Of 
those  with  previous  influenza  history  15.6  per  cent,  had  a  repeated 
attack,  while  of  the  remainder  without  previous  history  of  influenza 
10.9  per  cent,  were  attacked  in  1920.  They  conclude  that  no  marked 
immunity  to  influenza  exists  12  to  15  months  after  a  previous  attack, 
but  that  the  results  do  not  show  that  some  degree  of  immunity  may 
not  obtain  at  an  earlier  period. 

It  is  interesting  while  considering  the  subject  of  immunity  to  pay 
particular  attention  to  those  who  did  not  develop  the  disease  as  well  as 
to  those  who  did.  In  our  series  70  per  cent,  of  all  individuals  escaped 
the  disease  in  both  epidemics.  With  some  variation  this  figure  will 
hold  for  all  communities.  Or,  again,  among  those  who  had  the  disease 
in  1920,  75  per  cent,  had  not  had  it  in  the  preceding  waves. 

Hall  states  that  in  Copenhagen  at  the  Bispebjaerg  Hospital,  among 
the  500  patients  with  influenza  in  the  four  weeks  early  in  1920,  91.8 
per  cent,  had  not  had  the  influenza  during  the  1918-19  epidemic. 
H.  F.  Vaughan  found  in  a  review  of  2,500  cases  occurring  in  Detroit 
in  January,  1920,  that  84  per  cent,  had  never  had  the  influenza  before. 
The  true  significance  of  these  figures  cannot  be  recognized,  because 
we  are  not  informed  as  to  the  per  cent,  of  these  populations  attacked 
in  1918-19. 

We  observed  such  a  universal  distribution  of  influenza  during  the 
epidemic  period  that  it  is  frequently  assumed  that  all  individuals  are 
exposed  to  the  disease,  that  the  virus  must  enter  the  body  of  all  or 
nearly  all,  and  that  it  is  due  chiefly  to  a  relative  natural  immunity  that 
some  do  not  fall  victims.  Is  this  the  actual  state,  or  is  it  true  that  the 
distribution  of  the  virus  is  limited  to  about  one-third  of  the  population 
and  that  practically  all  of  those  who  are  actually  exposed  develop  the 
disease?  These  are  the  two  extremes;  more  probably  the  actual 
state  is  somewhere  between. 

This  question  cannot  be  definitely  answered,  and  yet  it  is  one  of 
extreme  importance,  particularly  with  regard  to  prevention  and  com- 
bat of  the  disease.  How  universally  is  the  influenza  virus  distributed 
during  pandemics?  What  proportion  of  the  population  is  actually 
exposed  by  invasion  with  the  virus?  What  proportion  of  actually 
exposed  individuals  develops  the  disease?     We  will  refer  to  this  again 

17 


210  INFLUENZA 

when  comparing  influenza  with  other  infectious  diseases,  but  it  is  of 
particular  interest  now  to  review  our  individuals  who  were  exposed  by 
sleeping  with  cases  of  influenza.  Fifty-five  per  cent,  of  all  individuals 
sleeping  in  the  same  bed  with  cases  of  influenza  in  1918  did  not  con- 
tract clinical  influenza.  Seventy  per  cent,  of  all  individuals  sleeping 
with  influenza  cases  in  1920  did  not  contract  the  disease,  in  recogni- 
zable form.  Sixty-nine  per  cent,  of  all  individuals  in  1920  who  had 
not  had  the  disease  previously  and  who  slept  with  cases  did  not 
develop  evidences  of  the  disease. 

It  is  difficult  to  conceive  of  a  degree  of  exposure  much  closer  than 
that  of  sleeping  in  the  same  bed  with  a  sick  individual.  And  yet  it  is 
equally  conceivable  that  many  individuals  sleeping  in  the  same  bed 
with  a  patient  were  not  penetrated  by  the  virus  of  influenza.  This 
does  not  aid  us  in  answering  our  question.  We  do  not  know  whether 
the  more  important  factor  is  that  of  a  natural  immunity  or  that  of 
absence  of  actual  invasion  by  the  virus. 

These  results  with  sleeping  contacts  form  an  interesting  link  in  the 
chain  of  evidence  started  during  1918  by  the  U.  S.  Navy  and  Public 
Health  Service,  and  reported  by  Rosenau  and  by  McCoy  and  others. 
These  experimenters  working  in  Boston  and  in  San  Francisco  carried 
out  inoculation  experiments  on  human  volunteers.  The  work  in 
Boston,  as  reported  by  Rosenau,  was  carried  on  with  100  volunteers 
from  the  Navy  between  the  ages  of  eighteen  and  thirty,  most  of  them 
between  eighteen  and  twenty-five;  all  of  them  entirely  well,  and 
with  the  exception  of  a  few  controls,  none  having  experienced  known 
attacks  of  influenza  previously.  First,  suspensions  of  thirteen 
different  strains  of  influenza  bacilH,  all  from  cases  of  influenza  during 
the  epidemic,  were  sprayed  into  the  nose,  eyes  and  throat  of  nineteen 
volunteers.  None  of  them  took  sick.  Next,  secretions  from  the 
mouth,  nose  and  throat  and  bronchi  of  acute  cases  of  influenza  were 
collected,  pooled,  and  without  filtration  sprayed  into  each  nostril, 
into  the  throat  during  inspiration,  and  onto  the  conjunctiva  of  each 
of  ten  volunteers.  None  of  them  took  sick.  Some  of  this  same  ma- 
terial was  filtered  through  a  porcelain  filter  and  administered  in  the 
same  manner,  with  similar  results.  One  cubic  centimeter  of  each  type 
was  administered  to  each  individual.  The  interval  between  the  time 
of  collection  and  time  of  inoculation  was  then  decreased  to  one  hour 
and  forty  minutes,  the  minimum  time  in  which  the  material  could  be 
transferred  from  hospital  to  experiment  station.  The  same  results 
were  obtained.  This  time  six  cubic  centimeters  were  administered  to 
each  individual.     Finally,  transfer  was  made  directly  with  swabs  from 


AN    EPlDKMlOLOtaC    STUDY  211 

tho  noso,  throat  ami  nasopharynx  of  one  individual  tf)  another  in 
nineteen  eases.     None  developetl  the  tlisease. 

The  next  series  of  experiments  consisted  in  an  attempt  to  inoculate 
volunteers  with  influenza  by  injecting  into  them  10  cc.  of  citratcd 
blood,  which  was  the  pooled  colhM'tioii  from  five  cases  of  acute  influ- 
enza. Ten  volunteers  were  inoculated.  None  took  sick.  Next,  the 
secretions  from  the  upper  respiratory  tract  of  acute  cases  were  injected 
subcutaneously  into  ten  volunteers,  each  receiving  3.5  cc.  This 
material  was  first  put  through  a  porcelain  filter.  None  took  ill.  In 
an  attempt  to  reproduce  the  disease  in  imitation  of  nature,  ten  in- 
dividuals were  exposed  to  cases  of  acute  influenza  in  hospital  wards. 
Each  volunteer  was  placed  very  near  to  the  patient,  shook  hands  with 
him,  talked  and  chatted  with  him,  for  five  minutes,  after  which  he 
received  the  patient's  breath  full  in  his  face  five  times  while  he  inhaled, 
and  finally  the  patient  coughed  five  times  directly  into  the  subject's 
face.  Each  volunteer  did  this  with  each  of  ten  different  patients,  all 
of  them  acutely  ill,  none  more  than  three  days  sick.  No  volunteers 
developed  the  disease.  All  cases  of  influenza  used  throughout  the 
period  of  these  experiments  were  t^^pical  acute  cases  selected  from  a 
distinct  focus  or  outbreak  of  the  disease.  Sometimes,  for  example, 
they  would  select  four  or  five  typical  cases  from  an  epidemic  in  a 
school  with  a  hundred  cases. 

In  February,  1919,  the  experiments  were  continued  at  Portsmouth, 
where  the  secretions  were  transferred  direct  from  individual  to  individ- 
ual. In  about  thirty-six  hours  half  of  the  number  came  down  with 
streptococcus  sore  throat,  but  not  with  influenza.  One  of  the  medical 
officers,  however,  who  had  been  very  active  in  the  experiments,  and 
who  had  come  into  intimate  contact  with  the  disease  since  early  in 
October,  but  w^ho  had  not  been  inoculated,  developed,  during  this 
experiment,  typical  influenza.  The  explanation  for  these  failures  is 
not  certain.  The  experiments  were  started  rather  late  after  the  onset 
of  the  epidemic,  and  the  volunteers  may  have  developed  some  im- 
munity, although  they  had  not  developed  the  disease.  Or,  they  may 
never  have  been  susceptible. 

McCoy  made  a  similar  series  of  experiments  in  San  Francisco,  using 
volunteers  who  so  far  as  known  had  not  even  been  exposed  to  the 
outbreak,  also  with  negative  results.  However,  many  of  these  latter 
had  been  "vaccinated  against  influenza"  with  a  mixed  vaccine. 

Wahl  and  his  co-workers  found  that  the  nasal  application  of  a 
filtrate  from  the  pneumonic  lung  of  an  individual  dead  with  typical 
influenza-bronchopneumonia  failed  to  call  forth  any  abnormal  symp- 


212  INFLUENZA 

toms  in  human  subjects.  The  apphcation  to  the  mucous  membrane 
of  the  nares  and  nasopharynx  of  five  healthy  men,  who  had  been 
inoculated  from  four  to  six  weeks  previously  against  influenza  with  a 
polyvalent  influenza  vaccine,  and  of  one  uninoculated,  of  freshly 
prepared  suspensions  of  four  different  live  strains  of  Bacillus  influenzae, 
even  in  massive  doses  failed  to  produce  any  abnormal  symptoms. 
The  implantation  of  living  suspensions  of  Bacillus  influenzae  produced 
no  material  alteration  besides  the  addition  of  the  influenza  bacillus 
itself.  When  experimentally  introduced  into  the  nasopharynx  of  men 
the  influenza  bacillus  exists  and  multiplies  for  a  considerable  length 
of  time,  two  weeks  or  more.  It  apparently  shows  much  resistance  to 
the  action  of  dichloramin  T. 

SECTION  VI. 
Influenza  and  Other  Diseases. 

Influenza  and  tuberculosis. — Following  the  1918  and  1920  epidemics 
of  influenza,  there  has  arisen  in  the  literature  some  controversy  regard- 
ing the  effect,  if  any,  of  influenza  on  tuberculous  individuals.  This 
has  centered  particularly  on  the  question  whether  tuberculosis  pro- 
duces some  degree  of  immunity  to  influenza,  and  whether  the  latter, 
on  the  other  hand,  predisposes  either  to  the  lighting  up  of  a  latent 
tuberculosis,  or  to  a  new  infection  with  the  tubercle  bacillus.  Keen 
observers  in  the  field  of  tuberculosis  who  have  had  apparently  equal 
opportunities  to  study  the  effects  of  the  pandemic  differ  radically  in 
their  conclusions. 

The  first  mention  of  consumption  following  influenza  was  made  in 
1580  by  Thomas  Short. 

After  the  1889-1893  epidemics,  Leichtenstern  recorded  that  the 
mortality  tables  of  all  countries  agree  in  showing  considerable  rise  in 
the  mortahty  from  pulmonary  tuberculosis  in  influenza  periods.  The 
clinicians  of  that  time  made  the  frequent  observation  that  the  course  of 
tuberculosis  in  the  lungs  is  markedly  and  unfavorably  influenced  by 
grip  and  its  pneumonic  complications.  Latent  quiescent  cases  often 
became  active,  and  healed  and  heahng  foci  broke  out  anew.  Afebrile 
cases  were  changed  to  the  hectic  type  and  frequently  hemoptysis  was 
induced.  In  London,  during  the  height  of  the  1889  epidemic,  the 
weekly  death  reports  from  phthisis  rose  to  double  the  avei-age.  The 
increase  in  death  rate  during  the  epidemic  period  was  not  limited 
entirely  to  tuberculosis,  but  there  was  almost  a  doubUng  of  deaths 
due  to  aU  acute  respiratory  infections.     After  the  cessation  of  the 


AN    EPIDEMIOLOGIC    STUDY  213 

epidemic,  however,  there  was  some  decrease  in  the  general  mortaUty, 
as  well  as  in  tho  mortality  from  respiratory  infections.  This  was 
especially  true  of  deaths  from  pulmonary  tuberculosis,  which  decreased 
to  such  an  extent  that  the  total  mortality  rate  for  the  year  for  this 
disease  was  little  greater  than  for  preceding  years. 

Similar  observations  have  been  made  following  the  1918  pandemic. 
Jordan  remarks  that  in  New  York  City  in  1918  during  the  two  weeks  of 
maximum  epidemic  mortality,  the  deaths  reported  from  pulmonary 
tuberculosis  numbered  430,  as  compared  with  264  for  the  corresponding 
weeks  of  1917.  Vaughan  and  Palmer  found  that  the  deaths  from 
tuberculosis  in  the  army  were  higher  in  the  autumn  of  1918  than  in  the 
two  previous  four  months'  periods,  the  death  rate  rising  from  18  per 
100,000  during  the  summer  to  46  per  100,000  in  the  autumn.  The 
rate  for  the  same  time  of  the  preceding  year  had  been  15  per  100,000. 
They  assume  that  the  most  plausible  explanation  for  this  increase  in 
deaths  is  that  dormant  and  incipient  cases  introduced  into  the  army 
during  the  preceding  year  had  accumulated  and  possibly  were  hastened 
into  the  acute  stage,  both  by  the  duties  of  camp  life,  and  the  prevalence 
of  the  epidemic  of  grip  and  pneumonia.  Quite  naturally  there  had 
been  from  the  time  of  the  first  assembling  of  troops  an  accumulation  of 
tuberculous  individuals,  inasmuch  as  such  men  were  not  discharged, 
but  were  kept  in  the  army  and  under  Government  control  and  super- 
vision. Sir  Arthur  Newsholme  in  reviewing  the  relationship  between 
influenza  and  tuberculosis  in  England  concludes  that  many  deaths 
from  tuberculosis  are  undoubtedly  hastened  during  an  influenza 
epidemic.  Abbott  wrote  of  the  epidemic  of  1889  in  Massachusetts 
that  the  chief  diseases  which  followed  in  its  train  and  were  intimately 
associated  with  it  were  bronchitis  and  peumonia,  and  that  phthisis 
when  already  existing  in  the  victim  of  the  attack  was  undoubtedly 
aggravated,  and  in  many  cases  a  fatal  termination  was  hastened. 
Baldwin  says  that  influenza  is  a  frequent  and  important  agent  in 
bringing  latent  tuberculosis  to  life.  "Allowing  for  mistakes  in  diagno- 
sis, influenza  must  be  classed  as  an  important  exciting  cause,  if  not 
a  true  predisposition." 

In  frank  opposition  to  the  foregoing  authorities,  Fishberg  claims 
that  influenza  has  had  no  effect  whatever  on  the  course  of  tuberculosis. 
He  says  that  a  large  proportion  of  tuberculous  patients  under  treatment 
in  New  York  City  in  1918-1919  contracted  the  disease  and  not  a  single 
one  succumbed.  This  appears  as  rather  an  inclusive  statement.  He 
goes  on  to  say  that  some  were  in  far  advanced  stages  of  the  disease, 
with  large  cavities  in  the  lungs,  and  yet  they  passed  through  the  acute 


214  INFLUENZA 

symptoms  and  recovered,  the  tuberculous  process  then  pursuing  its 
course  as  if  no  compHcating  disease  had  affected  them.  He  believes 
that  the  prognosis  was,  if  anything,  better  in  those  who  suffered  from 
tuberculosis  or  any  other  chronic  pulmonary  disease,  such  as  asthma, 
bronchitis,  emphysema,  bronchiectasis,  than  in  those  in  whom  the 
lungs  and  bronchi  had  been  apparently  in  healthy  condition.  Fishberg 
observes  that,  instead  of  lighting  up  the  tuberculosis,  the  influenza  runs 
a  milder  course  than  when  attacking  healthy  persons,  and  the  old  lung 
lesion  remains  in  about  the  same  condition  as  could  be  expected  if  no 
complicating  process  had  attacked  the  patient.  He  says  that  authors 
who  have  asserted  the  contrary  have  based  their  arguments  mainly  on 
the  facts  first,  that  many  tuberculous  patients  date  the  onset  of  their 
tuberculosis  as  concurrent  with  an  attack  of  influenza;  that  many 
patients  suffering  from  phthisis  state  that  ever  since  an  intercurrent 
attack  of  influenza  the  symptoms  of  tuberculosis  have  become  more 
pronounced ;  that  the  Pf eiff er  bacillus  has  been  found  quite  frequently 
in  the  sputum  of  tuberculous  patients,  especially  that  derived  from 
pulmonary  cavities ;  and  finally  that  in  some  countries  it  has  been  noted 
that  during  and  soon  after  an  epidemic  of  influenza  the  mortality  from 
tuberculosis  was  increased. 

He  believes  that  many  of  the  conditions  diagnosed  as  influenza 
have  been  no  more  than  ordinary  colds,  and  that  the  average  patient 
will  call  any  upper  respiratory  tract  infection  grip  during  or  around  the 
time  of  an  epidemic.  He  further  believes  that  a  misdiagnosis  of 
tuberculosis  is  frequently  made  in  influenza  convalescents  who  show 
some  signs  of  moisture  in  their  lungs  which  does  not  clear  up  for  some 
time,  causing  doubt  in  the  mind  of  the  examiner,  but  which  is  not 
truly  tuberculous  in  origin.  Fishberg  cities  P.  J.  Murphy,  Hawes, 
Armstrong,  McRae,  and  Dickinson,  as  well  as  Geiber  and  Schlesinger, 
in  Vienna,  and  Rickmann  and  Ladeck  in  Germany,  as  having  observed 
the  same  phenomenon  of  relative  insusceptibility  of  tuberculous 
patients  and  failure  of  influenza  to  hasten  the  progress  of  tuberculosis. 
He  also  calls  attention  to  the  low  incidence  of  influenza  in  tuberculosis 
sanatoria,  but  apparently  compares  this  incidence  with  the  incidence 
for  the  public  at  large,  and  not  with  that  in  similar  institutions  devoted 
to  the  care  of  invalids  with  diseases  other  than  tuberculosis,  or  with 
other  institutions  in  general. 

Amberson  and  Peters,  as  well  as  Minor,  take  sharp  exception  to  the 
statement  of  Fishberg,  and  the  former  have  collected  the  evidence 
against  Fishberg's  view.  They  first  point  out  that  a  comparison  of  the 
incidence  of  5.4  per  cent,  amoxig  hospitalized  tuberculous  patients  at 


AX    KPIDEMIOLOGIC    STUDY  215 

Chicago  cannot  be  compared  with  a  much  higher  incidence  of  the 

epidemic  in  the  various  mihtary  camps.  As  Heiser  has  pointed  out, 
the  mere  quartering  of  men  in  barracks  seems  to  have  a  tendency  to 
increase  the  risk  from  acute  respiratory  diseases.  Furthermore,  the 
incidence  at  some  sanatoria  was  low,  while  at  others  it  was  high,  nearly 
as  high  as  for  the  community  at  large.  In  Hawes'  report  of  the  epi- 
demic among  the  Massachusetts  sanatoria,  Lakeville  had  escaped 
entirely,  while  Rutland  which  consisted  chiefly  of  ambulatory  cases, 
less  easily  controlled,  had  an  influenza  incidence  of  18.3  per  cent, 
among  the  patients,  and  21.3  per  cent,  among  the  employees.  At 
Montefiore  Home,  the  proportion  of  tuberculous  patients  and  employees 
contracting  the  infection  was  practically  the  same  as  among  the  non- 
tuberculous  employees,  and  about  the  same  percentage  of  both  groups 
developed  evidence  of  bronchopneumonia. 

Still  another  fallacy  in  the  comparison  of  incidence  in  institutions 
and  the  like  is  proven  by  the  work  done  by  Jordan,  Reed  and  Fink,  who 
found  that  in  the  various  Chicago  telephone  exchanges  the  attack  rate 
varied  from  five  per  cent,  to  twenty-seven  per  cent.,  although  the 
working  conditions  were  approxiniately  the  same.  The  attack  rate 
in  one  section  of  the  students'  army  training  corps  in  Chicago  was  3.9 
per  cent.,  while  in  another  section  particularly  exposed  to  infection  it 
was  39.8  per  cent.  Similarly  Frost  found  the  incidence  in  Louisville, 
Kentucky,  to  be  15  per  cent.,  and  in  San  Antonio,  Texas,  53.3  per  cent. 
All  these  figures  show  the  difficulty  of  comparing  rates  for  various 
institutions  and  various  groups  of  individuals.  Although  Fishberg 
quoted  Rickmann  in  support  of  his  contention  that  influenza  has  no 
effect  whatever  upon  tuberculosis,  Amberson  and  Peters  used  his 
work  in  support  of  their  contention,  and  call  attention  to  the  fact  that 
in  thirty  out  of  forty  tuberculous  persons  reported  by  him  who  had 
contracted  the  grip,  the  attack  did  not  produce  any  aggravation  of  the 
lung  condition.  Presumably  it  did  in  the  other  ten.  If  even  25  per 
cent,  of  tuberculous  patients  who  contract  influenza  have  their  pul- 
monary condition  aggravated,  this  should  be  regarded  as  a  notable 
number.  According  to  Stivelman,  11.4  per  cent,  of  tuberculous  in- 
fluenza cases  died  at  IMontefiore  Home.  In  a  survey  of  convalescents 
from  the  Loomis  Sanatorium,  Amberson  and  Peters  found  that  seventy 
had  contracted  influenza,  or  5.7  per  cent,  of  the  number  surveyed,  and 
that  11.4  per  cent,  of  these  had  had  relapses  of  their  pulmonary  condi- 
tion, apparent]}'  due  to  the  acute  disease,  while  22.9  per  cent,  had  died 
from  the  intercurrent  infection.  2.8  per  cent,  were  deaths  due  to 
tuberculosis  after  convalescence  from  the  influenza. 


216  INFLUENZA 

Tubercle  baciUi  have  been  found  in  the  sputa  of  convalescent  grip 
patients,  whose  sputa  had  previously  been  negative,  by  Amberson  and 
Peters,  as  well  as  by  Berghoff,  at  Camp  Grant.  The  latter  found  that 
50  per  cent,  of  his  cases  showed  a  reactivation  and  a  positive  sputum 
after  an  attack  of  influenza. 

Amberson  and  Peters  agree  with  Fishberg  in  the  observation  that 
there  has  been  no  increase  in  the  general  mortality  from  tuberculosis 
within  the  recent  months,  and  suggest  as  an  explanation  the  possi- 
bility that  during  the  epidemic  enough  of  the  old  cases  were  carried 
off  to  account  for  a  temporary  lull  until  new  cases  developed,  or  others 
had  time  to  reach  later  stages  of  the  disease.  As  we  have  previously 
remarked,  Leichtenstern  observed  this  same  phenomenon  following 
the  1889-1890  epidemic. 

The  state  of  our  knowledge  of  influenza  and  tuberculosis  is  con- 
siderably clouded  by  divergent  opinions  such  as  those  quoted  above. 
To  further  complicate  the  picture,  there  are  other  authors  who  assume 
a  middle  ground  and  believe  that  there  is  some  truth  in  both  lines  of 
contention.  Thus,  Amelung  believes  that  the  morbidity  among  pa- 
tients with  pulmonary  tuberculosis  is  slight,  and  that  the  grip  takes  a 
milder  course  in  such  patients  than  in  the  non-tuberculous,  unless  the 
disease  is  far  advanced,  but  that  pulmonary  tuberculosis  may  and 
sometimes  does  follow  the  disease  in  patients  whose  lungs  were  previ- 
ously sound,  and  that  in  the  last  mentioned  cases  the  prognosis  is 
relatively  bad.  Peck  finds  that  in  some  tuberculous  patients  the 
disease  has  been  aggravated,  but  in  the  majority  the  intercurrent 
influenza  did  not  appear  to  have  been  the  causative  factor  in  the  acute 
exacerbation  of  the  tuberculosis. 

Debre  and  Jacquet  have  reviewed  the  European  literature  on  the 
subject  pro  and  con,  and  though  they  admit  that  there  are  exceptions, 
as  at  I'hopital  Tenon,  where,  in  a  barracks  reserved  entirely  for 
female  tuberculosis  patients  there  was  a  veritable  epidemic  of  grip, 
29  per  cent,  of  the  twenty-eight  being  attacked  in  a  few  days;  and  at 
the  sanatorium  de  La  Tronche,  where  83  per  cent,  took  ill  between  the 
25th  of  September  and  the  20th  of  October;  they  conclude  that  as  a 
rule  tuberculous  individuals  are  less  heavily  attacked  by  the  influenza 
than  are  the  nontuberculous.  As  they  suggest,  the  first  explanation 
that  comes  to  mind  is  that  the  tuberculous  are  isolated  in  the  hospitals 
where  general  hygienic  conditions  are  good,  but  we  have  all  seen  other 
institutions,  hospitals,  etc.,  in  which  the  inmates  were  not  spared  as 
they  were  in  tuberculosis  hospitals.  Furthermore,  in  certain  sanatoria, 
such  as  the  sanatorium  of  the  Cote  Saint- Andre,  and  Bligny,  and  several 


AN    EPIDEMIOLOGIC    STUDY  217 

German  sanatoria,  the  proportion  of  tuberculous  individuals  attacked 
was  very  much  less  than  that  of  the  professional  attendants,  the 
physicians  and  nurses.  Again,  whore  cases  have  occurred  in  these 
hospitals,  and  little  precaution  was  taken  to  prevent  its  spread,  very 
few  other  individuals  took  sick.  Finally,  many  have  noted  the  in- 
frequency  of  the  disease  even  in  those  tuberculous  individuals  who 
were  living  at  home.  It  has  been  suggested  that  rest  in  bed  from  the 
beginning  of  the  attack  explained  the  mildness,  or  that  the  immunity 
resulting  from  the  infection  with  pneumococcus,  streptococcus,  etc., 
in  tuberculous  individuals  explained  the  absence  of  pulmonary  com- 
plications. Marfan,  who  observed  this  same  phenomenon  in  1890, 
suggested  that  it  might  be  due  to  a  refractory  state  of  the  tubercle 
bacillus  against  the  virus  of  influenza.  Debr6  and  Jacquet  conclude 
that  none  of  these  explanations  is  satisfactory. 

Having  concluded  that  tuberculosis  does  protect  in  some  measure 
against  influenza,  Debr^  and  Jacquet  next  discuss  whether  the  latter 
has  increased  the  severity  of  tuberculosis  in  the  subjects  who  were 
already  tuberculous.  They  review  the  literature  and  make  their 
conclusions,  not  from  statistical  records,  but  from  general  observa- 
tions. They  consider  first  those  cases  of  phthisis  which  are  open  cases 
when  attacked,  and  second,  latent  tuberculosis.  Their  conclusion 
concerning  the  first  group  is  that  influenza  does  not  have  any  effect  on 
the  rapidity  of  evolution  of  the  tuberculous  process,  except  in  very 
rare  instances,  such  as  an  occasional  case  of  miliary  tuberculosis 
following  grip.  As  regards  latent  tuberculosis,  however,  they  do 
believe  that  the  intercurrent  acute  infection  does  cause  in  many  cases  a 
lighting  up  of  a  previously  entirely  dormant  tuberculosis.  It  seems 
rather  difficult  to  reconcile  the  two  ideas.  If  one  type  of  tuberculous 
individual  is  rendered  more  susceptible  to  the  ravages  of  consumption, 
it  would  seem  reasonable  to  expect  that  all  types  would  be  so  affected. 

The  greatest  difficulty  in  reaching  a  conclusion  regarding  the  effects 
of  influenza  on  tuberculosis,  and  vice  versa,  is  due  to  the  fact  that  the 
individuals  studied  are  in  all  stages  of  the  disease,  and  that  each  in- 
dividual reacts  differently  and  in  his  own  way.  Opinions  have  been 
based  chiefly  on  clinical  observations,  and  not  on  statistical  study  of 
large  series  of  cases,  while  from  the  nature  of  the  conditions,  even 
statistical  studies  would  not  be  without  great  fallacy. 

Armstrong,  found  in  a  survey  made  in  Framingham,  Massachusetts, 
that  16  per  cent,  of  the  entire  population  was  affected  with  influenza, 
but  only  4  per  cent,  of  the  tuberculous  group  in  the  community. 
Most  of  these  latter  were  of  the  arrested  type  and  were  going  about 


218  INFLUENZA 

taking  their  part  in  industry  and  exposed  to  the  same  degree  of  contact 
as  was  the  case  with  the  normal  population.  The  fatality  rate  was 
equally  in  contrast.  Armstrong  concluded  that  there  appeared  to  be 
a  relative  degree  of  protection  for  the  highly  tubercularized.  If  we 
accept  these  figures  at  their  face  value  we  must  conclude  then  either 
that  tuberculosis  offers  some  degree  of  protection  against  acute  influ- 
enzal infection,  or,  that  the  tuberculous  of  Framingham  have  been  so 
well  trained  in  sanitation  and  personal  hygiene,  as  a  result  of  the 
Framingham  demonstration,  that  they  have  been  able  to  protect 
themselves  against  the  grip.  In  the  latter  case  we  must  look  upon  the 
result  as  a  successful  demonstration  of  the  principles  of  preventive 
medicine.  Certainly  this  did  play  a  part,  to  the  extent  at  least  that 
individuals  knowing  themselves  to  be  infected  with  tuberculosis,  and 
knowing  themselves  to  be  in  the  presence  of  a  pandemic,  became  more 
wary  of  crowd  contact,  and  in  case  they  did  become  ill,  they  undoub- 
tedly went  to  bed  at  the  earliest  opportunity. 

If,  on  the  other  hand,  this  is  a  true  demonstration  of  relative 
immunity  in  a  chronically  infected  individual,  the  explanation  must  be 
sought  elsewhere.  Does  a  chronic  respiratory  infection  confer  a 
relative  degree  of  immunity  to  an  acute  respiratory  disease?  Do 
the  germs  already  on  the  premisies  exert,  so  to  speak,  "squatters' 
rights?"  Are  we  observing  an  example  of  non-specific  immunity  due 
to  local  preceding  infection?  Still  another  factor  may  play  an  im- 
portant role,  the  factor  of  race  stock.  The  excess  of  tuberculosis  in 
negroes,  for  instance,  over  that  in  whites,  is  in  some  localities  double 
or  treble,  while  various  observers,  as  Frost,  Brewer,  and  Frankel  and 
Dublin,  report  that  the  influenza  incidence  and  mortality  among 
negroes  was  decidedly  less  than  that  among  the  whites.  Winslow 
and  Rogers  found  that  in  Connecticut  the  proportion  of  influenza- 
pneumonia  deaths  is  lower  than  would  be  expected  among  persons  of 
native  Irish,  English  and  German  stock,  and  higher  than  was  to  be 
expected  among  Russian,  Austrian,  Canadian  and  Polish  stock,  whiel 
it  was  enormously  high  among  the  Italian.  Italians  are  notably 
insusceptible  to  tuberculosis,  while  the  Irish  are  much  more  prone  to 
infection  with  the  disease.  For  example,  in  Framingham,  where  the 
tuberculosis  incidence  rate  for  the  entire  population  was  2.16  per  cent., 
the  rate  in  the  Italian  race  stock  was  0.58  per  cent.,  and  in  the  Irish, 
4.80  per  cent.  In  Framingham  there  was  about  four  times  as  much 
influenza  among  the  Italians  as  among  the  Irish.  Is  this  apparent 
insusceptibility  of  certain  race  stocks  an  inherent  condition,  or  is  it 
dependent  chiefly  on  differences  in  living  conditions  and  in  age  pre- 


AN    EPIDEMIOLOGIC    STUDY  219 

valence  in  the  different  races?  Probably  it  is  chiefly  the  former. 
Frost,  for  instance,  found  that  ainonfj;  the  iU'fj;roes  the  incidence  of 
influenza  was  lowereven  thoughthe  Hving  conditions  were  much  poorer 
than  those  among  the  whites. 

Armstrong's  survey  has  also  thrown  some  light  on  the  effect  of  the 
influenza  on  previously  tubercularizcd  individuals.  In  a  survey  of 
700  individuals  who  had  had  the  acute  disease  there  were  ten  arrested 
cases  of  tuberculosis,  or  1.4  per  cent.  All  these  had  been  known  to  be 
arrested  cases  previous  to  the  epidemic,  and  in  none  of  them  did  the 
disease  appear  to  have  been  actively  and  permanently  lighted  up. 
Some  had  manifested  a  slight  activity,  but  all  seemed  to  be  on  the  way 
to  a  rearrest  of  the  disease.  On  the  other  hand,  thirteen  cases,  or  2 
per  cent,  of  the  700,  were  found  to  have  active  tuberculosis  which  had 
hitherto  been  undiagnosed,  and  an  additional  eight  cases,  with  indefi- 
nite broncho-pulmonary  signs,  were  designated  as  incipient  tuberculosis 
cases.  This  is  to  be  contrasted  with  an  incidence  of  active  tuberculosis 
in  the  pre-epidemic  examination  of  approximately  one  per  cent.  These 
figures  w^ould  indicate  an  increase  in  tuberculosis  incidence.  How 
may  this  be  explained?  The  acuracy  of  these  results  will  depend  on 
how  the  700  cases  were  selected.  If,  for  example,  individuals  who 
feared  tuberculosis  because  of  known  exposure,  requested  examination, 
the  results  might  be  influenced  by  their  inclusion. 

It  has  long  been  known  that  individuals  with  measles  will  not 
react  to  tuberculin  tests,  even  though  they  have  been  positive  before 
developing  the  measles,  and  though  they  will  become  positive  again 
after  recovery.  The  same  may  be  said  of  vaccination.  Individuals 
vaccinated  against  smallpox,  who  have  measles,  and  are  during  their 
illness  revaccinated,  will  not  show  an  immediate  reaction.  The  test 
will  remain  entirely  negative,  while  after  recovery,  the  immediate 
reaction  may  be  obtained.  Normally,  it  will  appear  in  95  per  cent, 
of  cases,  whOe  among  those  with  measles  the  phenomenon  remains 
absent  in  90  per  cent.  The  same  phenomenon  is  present  in  certain 
other  acute  illnesses,  particularly  scarlet  fever.  It  has  been  variously 
explained,  von  Pirquet,  who  was  the  first  to  observe  it  in  measles, 
believed  that  the  acute  disease  created  a  temporary  inability  to 
produce  antibodies,  and  therefore  designated  the  condition  by  the 
name  "anergic."  The  same  phenomenon  of  anergie  has  been  found 
recently  to  hold  in  the  case  of  influenza.  Debre  and  Jacquet,  Lere- 
boullet,  Bloomfield  and  Mateer,  as  well  as  Berliner  and  Schiffer,  have 
brought  forth  abundant  evidence  to  this  effect,  following  the  1918 
pandemic.     It  has  also  been  shown  by  CajTcl  and  others  that  there  is 


220  INFLUENZA 

a  diminution  of  typhoid  agglutinins  in  the  serum  of  influenza  patients 
vaccinated  against  typhoid.  The  agglutinin  titer  again  increases 
after  recovery.  It  is  true  that  the  agglutinin  titer  is  not  a  measure  of 
immunity,  but  it  is  frequently  used  as  such  and  serves  to  give  us  some 
information  on  the  subject.  If,  then,  influenza  is  an  anergic  disease, 
a  "maladie  anergisante,"  we  have  a  theoretical  explanation  of  the 
increase  in  severity  of  tuberculosis  following  the  acute  infection.  We 
have  long  observed  that  tuberculosis  frequently  follows  measles.  We 
have  recently  been  thoroughly  convinced  that  influenza  lessens  resist- 
ance to  secondary  infection  with  streptococcus,  pneumococcus,  and 
other  respiratory  tract  organisms.  Shall  the  tubercle  bacillus  be 
added  to  this  list?  During  the  1918  epidemic  we  saw  men  in  the  army 
camps  who  passed  through  an  attack  of  influenza-pneumonia  and  died 
within  a  few  weeks  from  tuberculous  pneumonia  or  miliary  tubercu- 
losis. These  men  had  previously  been  so  free  from  signs  of  their 
tuberculosis,  as  to  be  accepted  for  military  service  as  healthy  indivi- 
duals. The  number  of  these  cases  was  small,  to  be  sure,  but 
suflaciently  large  to  convince  us  that  there  do  exist  instances  in  which 
tuberculosis  is  tremendously  fired  by  an  intercurrent  influenza. 

If  we  may  judge  merely  by  the  balance  of  evidence  and  risk  any 
conclusions  from  such  conflicting  testimony,  we  may  sum  up  as  follows : 

1.  Great  variation  in  the  interaction  of  tuberculosis  and  influenza 
must  be  expected,  because  of  the  many  stages  at  which  the  tuberculous 
may  be  attacked,  because  of  the  altered  mode  of  living  of  known  con- 
sumptives, and  because  of  the  protected  life  of  most  of  them. 

2.  Phthisical  patients  as  a  group,  may  be  relatively  insusceptible 
to  influenza  infection.  This  may  be  due  to  the  tuberculous  process 
itself  or  to  some  extrinsic,  but  nearly  related  cause. 

3.  But  many  individuals  with  pulmonary  tuberculosis  do  get 
influenza. 

4.  And  the  disease,  having  been  contracted,  in  many  cases  hastens 
the  fatal  termination  of  the  tuberculous  process. 

5.  It  may  be  that  this  phthisical  exacerbation  occurs  more  fre- 
quently in  individuals  with  latent  tuberculosis,  individuals  who  are 
not  at  the  time  mobilizing  their  protective  antibodies. 

Other  infectious  diseases. — We  have  found  diversity  of  opinion 
regarding  the  relationship  between  influenza  and  tuberculosis,  and 
yet  the  latter,  being  as  a  rule  very  chronic  and  presenting  very  definite 
signs  which  may  easily  be  followed,  should  theoretically  be  a  disease 
in  which  the  results  of  study  would  be  quite  definite.  When  it  comes 
to  a  study  of  other  maladies  we  find  the  same  difference  of  opinion 
frequently  present. 


AN    EPIDEMIOLOGIC    STUDY  221 

It  has  been  the  experience  of  many  that  during  influenza  epidemics 
other  acute  specific  infectious  diseases  appear  to  diminish,  both  in 
number  of  cases  and  in  extent.  At  Camp  Sevier,  for  example,  two 
measles  wards  had  been  quite  constantly  full  of  patients  up  to  the  time 
of  the  fall  influenza  epidemic,  while  during  the  time  of  the  epidemic  one 
ward  appeared  sufficient  to  hold  all  cases  of  measles.  In  the  stress 
of  the  epidemic  this  difference  was  probably  more  apparent  than  real, 
and  certainly  is  not  to  be  taken  as  of  statistical  value. 

Vaughan  and  Palmer  report  for  all  troops  in  the  United  States 
that,  "Without  exaggeration  it  may  be  said  that  for  the  time  being  at 
least,  influenza  and  pneumonia  suppressed  other  infectious  diseases. 
Typhoid  fever  increased  to  a  barely  noticeable  degree.  The  death 
rate  from  this  disease  was  somewhat  higher,  but  the  total  number  is 
so  small  as  to  barely  warrant  comment,  and  not  to  justify  any  definite 
conclusion.  Scarlet  fever  and  malaria  were  both  lower  than  during 
the  summer.  In  fact,  there  was  but  one  scarlet  fever  outbreak  of  any 
importance  and  that  occurred  at  Camp  Hancock.  Within  two  weeks 
over  300  cases  were  reported  and  this  marks  the  largest  scarlet  fever 
epidemic  that  occurred  in  the  camps  in  this  country  at  any  time. 
Meningitis  increased  although  it  did  not  reach  the  prevalence  of  the 
previous  winter.  The  weekly  incidence  curve  for  all  troops  in  this 
country  suggests  that  meningitis  was  in  some  instances  a  sequel  to 
influenza.  The  greatest  meningitis  incidence  corresponds  with  the 
influenza  peak.  Diphtheria  showed  no  material  increase.  Deaths 
from  tuberculosis  were  higher  in  the  autumn  than  in  the  two  previous 
periods,  the  death  rate  rising  from  18  per  100,000  during  the  summer 
to  46  in  the  autumn.     The  rate  for  the  previous  winter  was  15." 

In  1889  Abbott  was  unable  to  find  satisfactory  evidence  of  a  con- 
nection between  influenza  and  other  epidemic  diseases,  although  as  he 
mentions,  such  connection  had  often  been  affirmed.  Instances  in 
support  of  each  position  were  to  be  found  in  the  literature  of  the  time. 

P.  Friedrich,  after  an  exhaustive  study  of  the  literature,  following 
the  1889  pandemic,  concluded  that  there  was  no  relationship  whatever 
between  the  incidence  of  influenza  and  other  acute  infections.  Wutz- 
dorff  reached  the  same  view  after  studying  the  various  diseases  during 
the  influenza  recrudescences  and  recurrences.  Finally,  Ripperger 
concluded  likewise. 

It  may  be  remarked  that  following  1918  there  have  been  several 
articles  written  concerning  the  relationship  between  influenza  and 
certain  other  diseases.  These  are  difficult  to  correlate  and  in  most 
instances  so  many  additional  factors  play  a  part  that  the  conclusions 


222  INFLUENZA 

drawn  are  perhaps  not  entirely  well  grounded.  Sylvestri  found  that 
in  his  experience  malaria  patients  escaped  the  influenza  during  the 
pandemic.  He  believes  that  it  was  the  malaria  rather  than  the  quinine 
which  was  responsible  for  the  apparent  immunity.  On  the  contrary 
others  have  observed,  if  anything,  an  increase  in  malarial  patients. 

Frankel  and  Dublin  found  that  daring  the  pandemic  period  deaths 
from  whooping  cough  increased.  The  difficulty  of  differentiating 
between  whooping  cough  and  influenza  as  a  cause  of  death  is  apparent. 

It  seems  quite  certain  that  deaths  from  organic  diseases  of  the 
heart  increase  during  and  following  influenza  epidemics  and  are  due 
probably  to  the  inability  of  the  weakened  patients  to  resist  the  added 
burden.  Frankel  and  Dublin  found  an  increase  in  deaths  from  this 
cause.     This  was  also  observed  to  be  true  in  Spain  and  other  localities. 

Jordan  has  compared  the  curves  of  influenza  with  those  of  acute 
coryza  among  school  children  of  Chicago  and  finds  that  the  period  of 
highest  incidence  of  colds  in  October,  1918,  occurred  in  the  second 
week  of  school  and  that  it  preceded  the  corresponding  period  of  influ- 
enza by  seven  weeks.  There  were  three  peaks  in  the  curve  for  colds 
and  only  two  in  that  for  influenza.  The  period  of  highest  incidence  of 
colds  follows  the  first  peak  of  the  influenza  curve  by  one  week,  while 
during  the  week  of  greatest  prevalence  of  influenza  there  is  a  sharp  fall 
of  the  number  of  cases  of  colds.  The  third  peak  for  colds  occurred 
one  week  after  the  height  of  the  influenza  curve.  As  a  rule  the  colds 
curve  runs  at  a  higher  level  than  that  for  influenza.  A  striking  fact  is 
that  the  portion  of  the  curve  for  influenza  contained  within  the  period 
November  23d  to  December  7th,  is  almost  the  exact  opposite  of  the 
corresponding  portion  in  the  curve  for  colds.  How  much  of  this  is  due 
to  the  factor  of  diagnosis  is  difficult  to  say. 

Encephalitis  lethargica. — It  is  not  within  the  scope  of  our  report  to 
discuss  in  detail  this  disease.  Its  apparent  relationship  with  influenza, 
in  point  of  time,  if  not  otherwise,  calls  for  special  mention.  In  1712  a 
disease  followed  a  pandemic  of  influenza,  occurring  particularly  in 
Germany,  where  it  was  known  under  the  name  of  "Tubingen  Sleeping 
Sickness."  In  the  spring  of  1890,  according  to  Netter,  a  disease  of 
similar  character  called  "Nona"  was  distributed  especially  in  Northern 
Italy  and  Hungary  and  scattered  more  or  less  diffusely  over  a  large 
part  of  Europe.  Preceding  the  last  influenza  pandemic  the  disease 
was  first  reported  in  Vienna  in  the  winter  of  1916-17.  Cases  were 
seen  in  Paris  in  February  and  March,  1918,  and  the  first  official  report 
of  the  disease  in  England  seems  to  have  been  on  January  26,  1918.  In 
the  spring  of  1918  there  were  168  officially  reported  cases  in  England 


AN    EPIDEMIOLOGIC    STUDY  223 

with  37  deaths.  The  disease  seems  to  have  disappeared  there  in  June, 
1918,  and  reappeared  in  the  autumn  of  the  same  year.  The  first  cases 
in  the  United  States  were  reported  by  Pothier  at  Camp  Lee,  Va.  Fol- 
lowing the  great  influenza  pandemic  cases  of  lethargic  encephalitis 
have  appeared  in  all  parts  of  the  world.  It  has  been  present  in  England, 
France,  Belgium,  Switzerland,  Austria,  Greece,  Italy,  pnd  other  coun- 
tries of  Europe,  South  America,  Mexico,  the  United  States, 
Australia,  Queensland,  New  South  Wales,  and  Algiers.  There  was  an 
increase  of  encephalitis  lethargica  concomitant  with  the  increase 
of  influenza  in  the  early  months  of  1920.  Thus,  in  Switzerland  440 
cases  were  reported  during  February,  1920.  The  1920  epidemic  of 
influenza  in  that  country  had  almost  ceased  by  the  middle  of  March, 
while  that  of  lethargic  encephalitis  had  greatly  decreased.  One 
hundred  and  forty-one  cases  of  the  latter  disease  appeared  in  the 
canton  of  Zurich  alone. 

Is  epidemic  encephalitis  a  disease  sui  generis  or  is  it  a  form  of 
influenza? 

The  consensus  of  opinion  has  been  that  it  is  a  separate  disease. 
There  is,  however,  no  way  of  telling  how  close  is  the  relationship  to  the 
influenza  itself.  If  lethargic  encephalitis  is  a  sequel  to  influenza,  is  it 
caused  by  the  same  germ?  Flexner  points  out  that  in  1916,  when  the 
first  cases  of  encephalitis  appeared  or  at  least  were  recognized  in  Austria, 
the  epidemic  of  influenza  had  not  yet  appeared.  In  England,  France 
and  the  United  States  the  epidemics  of  the  two  diseases  were  more  or 
less  coincidental.  He  believes  that  little  w^eight  can  be  given  the  sup- 
posed coincidence  of  influenza  and  the  "sleeping  sickness"  of  1712,  and 
that  it  is  highly  improbable  that  the  semi-mysterious  affection,  "nona," 
which  dates  from  1890  was  definitely  a  sequel  of  influenza.  He  con- 
cludes that  the  outbreak  of  encephalitis  either  antedated  the  pandemic 
of  influenza  of  1918,  or  that  the  two  diseases  more  or  less  overlapped; 
that  is,  although  probabh^  quite  by  accident,  they  prevailed  concur- 
rently. He  prefers  for  the  time  being  at  least  to  regard  them  as  inde- 
pendent diseases. 

Crookshank  believes  that  encephalitis  lethargica  is  a  distinct  dis- 
ease, but  that  it  occurs  frequently  as  an  antecedent  of  or  co-incident 
with  influenza,  together  with  increase  in  the  existence  of  poliomj'elitis 
and  certain  other  diseases. 

Nevertheless  the  association  in  point  of  time  and  place  between 
influenza  and  lethargic  encephalitis  cannot  be  lightly  overlooked.  As 
we  have  seen,  Flexner's  criticism  that  encephalitis  antedated  the 
influenza  is  not  valid,  because  the  latter  was  present  in  1916.  We 
must  await  fuller  evidence  on  this  subject. 


224  INFLUENZA 

SECTION  VII. 

COMPAKISON  OF  INFLUENZA  WITH  OtHER  EpIDEMIC  DISEASES. 

A  certain  amount  of  knowledge  concerning  the  epidemiology  of 
influenza  may  be  gained  by  a  comparison  of  the  epidemic  features  of 
that  disease  with  those  of  other  epidemic  diseases,  particularly  measles 
and  the  exanthemata,  meningitis,  the  plague,  and  certain  diseases  of 
the  lower  animals.  Influenza  is  described  as  a  disease  with  distinctive 
epidemiologic  characteristics,  the  chief  of  which  are  found  only  in 
epidemic  spreads.  Thus  one  of  the  fundamental  characteristics  of 
these  epidemics  is  supposed  to  be  the  primary  type  of  wave,  the  wave 
characterized  by  rapid  rise,  quasi-symmetrical  evolution,  and  a  con- 
centration closely  grouped  around  the  maximum.  "This  is  found 
in  no  other  disease.  In  no  other  type  of  epidemic  does  the  curve  rise  as 
rapidly  to  a  peak  or  fall  as  swiftly,  nor  is  the  epidemic  completed  in  as 
short  a  time." 

The  secondary  type  of  curve,  that  which  is  more  frequently  found  in 
recurring  influenza  epidemics,  characterized  by  a  more  gradual  ascent, 
a  still  more  gradual  decline  and  a  longer  duration,  is  found  frequently 
in  the  curves  for  other  diseases;  it  is  much  less  characteristic.  We 
shall  attempt  by  a  comparison  of  epidemic  influenza  with  these  other 
diseases  to  explain  the  cause  for  this  characteristic  primary  curve,  so  as 
to  gain  a  further  insight  into  the  epidemic  features  of  the  disease. 

There  are  certain  characteristics  held  by  epidemic  influenza  in 
common  with  other  diseases.  There  are  certain  resemblances  between 
it  and  epidemic  meningitis;  in  certain  ways  it  resembles  measles  and 
there  are  some  points  of  similarity  to  the  pneumonic  form  of  plague. 
The  fact  that  it  cannot  be  compared  with  one  of  these  diseases  to  the 
exclusion  of  the  others  renders  deductions  more  complicated. 

Epizootics. — Soper  has  written  at  some  length  on  a  comparison  of 
influenza  in  man  with  the  so-called  influenza  among  horses.  The 
close  resemblance  in  many  features  is  striking. 

Epizootics  of  a  disease  apparently  resembling  influenza  have  been 
described  among  horses  from  before  the  Christian  Era.  A  disease 
believed  to  have  been  influenza  was  recorded  as  having  occurred  B.C. 
among  horses  in  Sicily.  According  to  Parkes  the  epidemic  which 
attacked  the  army  of  Charlemagne  in  876  attacked  at  the  same  time 
dogs  and  birds.  Finkler  describes  an  epizootic  among  horses  in 
1404  A.D.  There  were  other  epizootics  in  1301,  1711  and  1870  to 
1873.     In  1901  a  severe  outbreak  occurred  in  America,  and  one  has 


AN    EPIDEMIOLOGIC    STUDY  225 

also  been  described  by  Mathers  as  occurring  in  Chicago  in  the  winter  of 
1915-16.  These  epidemics  of  a  disease  clinically  resembling  influenza 
have  frequently  occurred  among  horses  at  the  same  time  with  true 
epidemics  of  influenza  in  man.  Nevertheless  there  has  been  no  clear 
cut  evidence  to  prove  that  the  disease  is  the  same. 

Leichtenstern  discusses  the  incidence  of  respiratory  disease  among 
animals,  particularly  household  pets  during  epidemics  of  influenza. 
He  comes  to  the  conclusion  that  human  influenza  is  a  disease  limited 
entirely  to  the  human  race  and  having  no  connection  with  animal 
disease.  This  is  particularly  true  with  regard  to  diseases  reported 
among  cats,  dogs,  canaries  and  other  captive  birds.  He  also  believes 
that  the  epizootics  among  horses  which  have  been  reported  from  time 
to  time  as  occurring  with  influenza  epidemics  have  nothing  to  do  with 
the  disease  in  man.  The  symptoms  are  frequently  very  similar,  but 
epizootics  have  frequently  occurred  at  times  when  there  was  no  epi- 
demic of  disease  among  humans. 

Abbott  concluded  that  during  the  great  horse  epidemic  of  1872 
which  bore  a  strong  resemblance  to  influenza  the  disease  was  not 
unusually  prevalent  among  men  except  in  a  few  limited  localities; 
while  other  infectious  diseses,  such  as  measles,  small  pox,  scarlet  fever 
and  cholera  infantum  were  unusually  prevalent  in  that  year. 

Soper  writes  that,  "Economically,  influenza  is  the  most  important 
disease  of  horses  in  temperate  climates.  The  mortality  among 
remounts  has  been  many  times  greater  from  influenza  than  from  all 
other  diseases  put  together.  It  is  estimated  that  over  25,000  horses 
purchased  by  the  British  Government  in  America  and  Canada,  during 
two  years  of  the  war,  died  in  those  countries  while  awaiting  shipment 
to  Europe.  In  a  circular  issued  January  12,  1918,  by  the  Surgeon 
General  of  the  United  States  Army  to  the  veterinarians  of  remount 
depots,  it  was  stated  that  the  losses  from  influenza  among  American 
army  horses  amounted  to  over  $100,000  a  week.  The  disease  spoken 
of  as  influenza  in  the  horse  has  many  other  names.  It  is  commonly 
called  pink-eye,  shipping  fever,  stable  pneumonia  and  bronchitis. 
By  some  influenza  is  not  believed  to  be  a  single  disease,  but  a  group 
of  diseases.  By  others  it  is  considered  to  be  a  definite  entity,  varying 
in  its  symptom  complex  at  different  times  and  with  various  horses. 
Infectious  laryngitis  and  infectious  pharyngitis  seem  to  be  independent 
diseases.  Two  forms  of  influenza  are  generally  distinguished: 
catarrhal  and  pectoral." 

Even  after  the  last  pandemic  of  influenza  the  question  has  again 
arisen  as  to  the  identity  of  the  disease  among  animals.     Orticoni  and 

IS 


226  INFLUENZA 

his  co-workers  observe  that  there  was  an  extensive  epizootic  among 
horses  at  the  time  of  the  1918  epidemic  in  the  area  which  they  had 
under  observation.  There  have  been  other  similar  reports.  The 
popular  press,  during  the  height  of  the  1918  spread,  reported  that  there 
was  a  highly  fatal  influenza  infesting  the  monkeys  of  South  Africa 
and  that  the  baboons  were  dying  in  scores,  their  dead  bodies  being 
found  on  the  roadsides  and  in  the  vicinity  of  homesteads.  Another 
report  tells  of  the  influenza  decimating  the  big  game  in  Canada,  and 
yet  another  tells  of  the  havoc  wrought  among  the  buffalos  and  other 
animals  in  the  United  States  National  Parks.  These  reports  have  not 
been  corroborated  by  scientific  observations. 

Soper  has  analyzed  the  subject  of  so-called  influenza  among  horses. 
He  finds  that  the  disease  is  quite  generally  distributed,  that  it  has 
many  points  of  close  similarity  to  the  influenza  of  man,  but  that  it  is  a 
distinct  and  separate  disease.  The  two  diseases  are  not  identical  and 
neither  can  be  transmuted  into  the  other. 

"Briefly,  the  symptoms,  as  stated  in  a  recent  publication  of  the 
United  States  Department  of  Agriculture,  are  sudden  onset;  fever  in 
some  cases  preceded  by  chill;  great  physical  prostration  and  depression 
of  nervous  force;  sometimes  injected  mucous  membranes,  especially 
those  of  the  eye,  and  loss  of  appetite.  In  uncomplicated  cases  the 
fever  abates  after  about  a  week  and  there  is  a  general  restoration  to 
health.  Pneumonia  is  one  of  the  frequent  complications  and  is  always 
serious.  The  death  rate  varies  between  two  and  seven  per  cent. 
The  most  usual  form  is  the  catarrhal  type.  The  attack  may  last  only 
two  or  three  days;  in  other  cases  the  course  may  extend  to  two  weeks, 
in  which  event  it  takes  the  animal  a  long  time  to  get  well.  Horses 
which  have  passed  through  this  form  of  disease  may  be  considered  to 
have  recovered  two  weeks  after  the  disappearance  of  the  fever. 

"The  diagnosis  of  influenza  depends  as  much  upon  its  epidemi- 
ological aspects  as  upon  the  symptoms.  Law  bases  it  on  the 
suddenness  of  the  attack,  its  epizootic  character,  the  numbers  attacked 
in  rapid  succession  and  over  a  large  area  as  compared  with  ordinary 
contagious  pneumonia,  the  sudden  and  extreme  prostration,  the  mild- 
ness of  the  average  case,  the  congestion  of  the  upper  air  passages,  the 
watering  and  discoloration  of  the  eyes,  and  the  history  of  the  case. 
Points  of  interest  in  the  history  are  the  arrival  of  the  infected  horses 
within  a  few  days  from  an  infected  place,  or  coming  through  such  a 
place,  or  the  attacking  of  new  arrivals  in  a  previously  infected  stable, 
or  the  known  advance  of  the  disease  toward  the  place  where  the 
patients  are  located." 


AN    EPIDEMIOLOGIC    STUDY  227 

Soper  found  that  the  progress  of  tho  opidoniic  of  1872-73  among  thv. 
horses  in  this  country  was  as  generahzod,  but  much  slower  than  the 
progress  of  the  recent  pandemic  among  human  beings,  the  rapidity 
of  progress  corresponding  with  the  rapidity  of  the  transport  of  the 
horses  at  that  time.  Just  as  we  have  found  in  the  case  of  influenza  so 
also  at  that  time  the  spread  only  followed  lines  of  communication  and 
actual  contact  between  horses. 

It  is  highly  interesting  that  attempts  to  transfer  the  disease  from 
horse  to  horse  experimentally  met  with  the  same  degree  of  failure  that 
was  experienced  in  similar  attempts  to  transfer  influenza  experi- 
mentally from  man  to  man.  In  fact  Lieut.  Col.  Watkins  Pitchford 
of  the  British  Army  Veterinary  Corps  in  a  report  in  July,  1917,  stated 
that  it  was  impossible  to  produce  infection  experimentally.  Nose 
bags  were  kept  upon  horses  with  profuse  nasal  discharges  and  high 
temperature,  and  these  nose  bags  were  then  used  to  contain  the  food 
of  other  horses  without  infection  taking  place. 

There  are  several  other  points  of  resemblance  between  horse 
influenza  and  human  influenza.  The  mortality  from  influenza  among 
horses  is  under  ordinary  circumstances  between  two  and  seven  per 
cent.,  and  is  highest  in  horses  worn  out  by  fatigue  after  a  long  railroad 
journey,  among  fat  horses  out  of  condition,  and  among  horses  which 
have  been  driven  after  they  were  sick.  The  death  rate  in  the  simple 
catarrhal  form  of  influenza  rarely  exceeds  one-half  of  one  per  cent, 
while  in  the  pectoral  form  it  is  never  less  than  four  or  five  per  cent, 
and  may  reach  16  per  cent.  The  only  measure  of  prevention  which 
has  been  found  wholly  satisfactory  is  strict  isolation.  Usually  in- 
fluenza occurs  in  horses  who  have  newly  arrived  in  a  stable  from  else- 
where. Practically  all  the  newly  arrived  horses  and  country  horses 
are  almost  alone  susceptible.  Soper,  who  has  studied  the  records, 
such  as  they  are,  in  the  army  veterinary  corps,  and  also  the  records 
from  the  Bureau  of  Animal  Industry,  concludes  that  they  show  nothing 
to  indicate  that  any  general  epizootic  of  influenza  occurred  among 
horses  during  the  year  1918  corresponding  to,  or  connectable  with  the 
pandemic  of  influenza  among  human  beings.  There  was  influenza 
among  the  horses,  but  he  does  not  think  it  was  extensive  enough  to 
be  allied  with  influenza  among  human  beings.  He  concludes  that 
there  are  two  types  of  influenza  among  horses,  first  a  mild  form  which 
nearly  all  horses  get  when  transferred  to  a  contaminated  stable,  after 
which  there  develops  immunity,  and  the  second  type,  a  true  epizootic 
which  may  sweep  the  entire  country,  attacking  practically  every 
horse.     A  most  suggestive  result  of  his  study  lies  in  the  fact  that 


228  INFLUENZA 

predisposing  influences  play  a  most  important  part  in  the  production 
of  serious  influenza  among  horses. 

Aside  from  noting  a  certain  similarity  between  the  epizootic  of 
so-called  influenza  in  horses  and  influenza  as  we  know  it  in  man,  we 
cannot  acquire  much  additional  information  concerning  influenza 
itself  from  a  consideration  of  this  subject.  The  important  conclusion 
is  that  in  several  of  the  most  important  epidemiologic  features  the  two 
diseases  are  similar  and  that  the  study  of  human  influenza  may  be 
furthered  by  critical  studies  of  influenza  in  horses.  We  shall  attempt 
to  demonstrate  that  influenza  in  a  similar  manner  is  not  unlike  other 
epidemic  diseases. 

Asiatic  cholera. — There  are  those  who  claim  that  the  disease  should 
be  compared  with  Asiatic  cholera  which  remains  constantly  endemic 
on  the  banks  of  the  Ganges  and  at  intervals  spreads  from  there  through- 
out Indo-China,  and  formerly  at  times  throughout  the  civilized  world. 
Those  who  compare  influenza  with  this  disease  believe  that  this  is 
additional  evidence  in  favor  of  a  single  focus  of  endemicity  of  influenza. 

Epidemic  meningitis. — On  the  contrary  the  disease  may  well  be 
compared  with  epidemic  meningitis.  The  germ  of  this  disease,  dis- 
tributed throughout  the  world,  is  usually  in  an  avirulent  form  and 
produces  no  epidemic  of  meningitis.  Only  an  occasional  case  arises. 
There  are  certain  localities  in  which  the  disease  is  particularly  prevalent 
at  all  times.  We  may  speak  of  these  as  endemic  foci,  but  must  remem- 
ber that  at  the  same  time  the  virus  is  distributed  elsewhere.  Thus 
South  Carolina,  Missouri  and  Kansas  have  been  shown  to  be  localities 
in  which  meningitis  has  been  more  or  less  widely  distributed  for  some 
years. 

We  can  carry  the  analogy  still  farther.  During  the  concentration 
of  forces  early  in  the  war,  camps  were  established  at  Columbia,  S.  C. 
and  at  Fort  Riley,  Kansas.  In  these  camps,  Jackson  and  Funston, 
there  very  rapidly  developed  quite  extensive  epidemics  of  cerebrospinal 
meningitis.  Here  and  in  Camp  Beauregard,  the  incidence  of  the 
disease  was  out  of  all  proportion  to  that  in  the  other  camps.  Just 
as  the  exaltation  of  virulence  of  the  influenza  virus  has  been  favored  by 
gross  changes  in  the  environment,  the  occupation,  the  density  of,  and 
the  disease  incidence  in  the  host  as  a  community,  so  also  do  these 
appear  to  have  been  factors  in  the  development  of  a  meningitis  preva- 
lence in  the  army.  It  was  more  prevalent  in  those  camps  situated  in 
the  territories  where  the  disease  was  particularly  endemic,  but  was  also 
present  in  all  camps.  Had  the  meningococcus  been  able  to  assume 
the  high  degree  of  virulence  and  invasiveness  possessed  by  the  influenza 
virus  it  is  reasonable  to  assume  that  a  pandemic  spread  would  have 


AN    KPIDEMIOLOGIC    STUDY  229 

begun  in  one  of  the  two  or  three  camps  where  the  disease  was  especially 
prevalent.  It  would  have  spread  thence  and  have  attacked  those 
camps  in  which  a  mildly  virulent  meningococcus  had  already  been 
causing  disease.  Just  as  in  influenza  the  pandemic  spread  would 
have  been  due  not  to  the  universally  distributed  virus,  but  to  the  one 
or  few  which  finally  acquired  the  greatest  exaltation  of  virulence. 

We  see  then  that  the  followers  of  both  theories — that  of  the  single 
focus,  and  that  of  an  extensive  distribution — can  quote  other  infectious 
diseases  in  support  of  their  theory,  but  the  evidence  in  favor  of  simi- 
larity to  Asiatic  cholera  is  not  complete.  The  disease  is  not  similar. 
The  mode  of  transmission  is  entirely  different.  The  infection  is  chiefly 
of  the  gastro-intestinal  tract,  while  that  in  influenza  is  chiefly  respira- 
tory. Since  1816  there  have  been  five  pandemics  of  Asiatic  cholera, 
the  last  occurring  in  1883  and  all  of  them  traceable  to  a  primary  focus 
in  India.  Frequently  it  was  carried  from  India  by  the  faithful,  to 
Mecca  and  from  there  was  readily  distributed  throughout  Europe. 
In  the  last  pandemic  the  disease  spread  throughout  the  old  world  and 
reached  New  York  harbor,  but  was  refused  admission. 

Plague. — The  similarity  in  clinical  symptomatology,  in  gross 
pathology  and  the  apparent  similarity  in  manner  of  spread  and  epi- 
demic features  between  influenza  and  the  pneumonic  form  of  plague 
has  suggested  to  some  that  the  best  comparison  should  be  made  with 
the  latter  disease.  Here  again  is  a  disease  which  is  endemic  in  Asia 
and  spreads  elsewhere  only  at  intervals.  If  we  go  back  into  the  history 
of  the  plague  we  will  discover  that  formerly  it  was  distributed  more  or 
less  throughout  the  civilized  world.  The  plague  is  supposed  to  have 
been  known  to  the  children  of  Israel  at  the  time  of  the  exodus  from 
Egypt.  The  Eg^^pt  of  the  Pharaohs  was  a  country  of  great  salubrity. 
Hygienic  measures  were  excellent.  The  inhabitants  built  aqueducts, 
disposed  of  their  dead  hygienically,  reared  temples,  maintained  law 
and  order,  developed  the  elements  of  literature  and  science  and  devised 
and  employed  simple  machinery.  But  as  early  as  the  exodus,  Egypt 
had  lost  its  salubrity.  This  is  indicated  by  many  passages  in  the 
Bible.  The  plague  was  present  in  that  country  during  this  period. 
Sticker  believes  that  the  pest  among  the  Philistines  spoken  of  in  the 
First  Book  of  Samuel,  when  the  captured  army  was  returned  with  five 
golden  emerods  and  five  golden  mice,  was  the  bubonic  plague. 

Thucydides  describes  a  plague  in  Athens  occurring  before  Christ. 
This  is  generally  believed  to  have  been  "the  plague."  The  time  of  the 
earliest  appearance  of  the  disease  in  Italy  is  not  known  but  it  was  well 
established  there  in  the  first  century  of  our  era.  The  plague  was  ende- 
mic in  Italy  at  that  time  and  it  developed  in  epidemic  form  with  each 


230  INFLUENZA 

increase  in  susceptible  material.  At  about  68  A.D.  the  disease  spread 
over  the  whole  of  Asia,  Northern  Africa  and  Europe.  Exacerbations 
of  the  disease  are  described  in  the  years  80,  88  and  92  A.D.  In  Rome 
they  occurred  in  102,  107  and  117  A.D.  The  disease  was  present  in 
Wales  in  114  A.D.  In  167  an  unusually  severe  outbreak  of  the  plague 
occurred  in  Rome.  There  were  other  outbreaks  in  the  Roman  army 
in  173,  175  and  178.  Had  we  the  space  to  record  here  the  history  of  the 
plague  we  would  find  that  the  disease  was  widely  distributed  through- 
out Europe  for  several  hundreds  of  years,  that  it  was  particularly 
prevalent  in  certain  areas  and  that  at  intervals  it  spread  from  one  or  a 
few  foci,  throughout  the  continent. 

We  can  compare  the  epidemic  features  of  influenza  with  these  other 
contagious  diseases,  but  we  will  always  find  some  points  of  difference 
from  one  or  another.  Let  us  consider  again  for  a  moment  epidemic 
meningitis.  There  is  no  combination  of  predisposing  causes,  environ- 
mental, meteorologic  or  bacteriologic  which  will  produce  epidemics  of 
cerebrospinal  meningitis  in  the  absence  of  the  meningococcus  itself. 
The  organism  causing  the  disease  must  be  present  before  the  disease  will 
occur.  The  specificity  of  the  invading  organism  in  the  different 
diseases  will  always  produce  some  variation  among  the  epidemiologic 
features.  Other  things  being  equal,  that  locality  in  which  this  germ 
isjmost  extensively  distributed  will  be  the  locality  in  which  epidemics, 
when  they  do  break  out,  will  be  most  entensive. 

In  the  case  of  our  army  camps,  those  individuals  carrying  the 
disease  virus  from  the  endemic  foci  to  the  camps  were  not  the  ones 
who  fell  ill.  Generally  it  was  those,  coming  from  other  areas  in  which 
meningitis  was  not  extensively  distributed  and  who  had,  therefore, 
not  acquired  an  increased  resistance  to  the  disease,  who  fell  ill.  But 
after  the  disease  had  acquired  increased  virulence  at  Camp  Jackson, 
not  only  did  it  occur  in  the  troops  at  that  camp,  but  it  also  became 
quite  extensive  throughout  the  civilian  population,  presumably 
among  those  who  had  previously  been  exposed  to  it  in  its  endemic  form. 

In  our  comparison  of  influenza  with  other  infectious  diseases  we 
wish  to  show  particularly  that  the  disease  is  not  in  a  class  by  itself, 
but  that  its  epidemiologic  features  are  not  unlike  those  of  other  res- 
piratory infections,  that  the  manner  of  spread  and  the  mode  of  infec- 
tion are  similar  to  those  of  the  other  diseases.  Nothing  unusual  or 
unknown  need  be  called  into  use  in  explaining  any  differences.  Those 
differences  that  very  palpably  exist  can  be  explained  by  facts  which 
we  already  know.  Leichtenstern,  thirty  years  ago,  believed  that  the 
disease  was  similar  in  its  manner  of  spread  to  other  infectious  diseases. 


AN  p:pidemiologic  study  231 

He  observed  this  particularly  in  the  earhest  and  the  latest  phases  of 
epidemic  spreads  where  cases  were  scattered.  He  saw  that  in  house- 
holds the  disease  attacked  some  and  spared  others  even  of  those  inti- 
mately connected  with  the  sick,  just  as  was  the  case  in  diphtheria  or 
meningitis.  He  writes:  "Comparing  these  later  periods  the  disease 
evidences  the  same  contagious  characteristics  as  the  other  endemic 
contagious  diseases,  such  as  scarlet  fever,  measles,  diphtheria,  epidemic 
cerebrospinal  meningitis,  etc." 

Parkes  made  very  similar  observations  even  before  the  1889 
epidemic. 

Measles. — A  comparison  of  influenza  and  measles  will  offer  some 
explanation  of  the  differences  between  the  epidemic  constitution  of 
the  former  and  that  of  the  other  respiratory  diseases. 

We  are  accustomed  to  think  of  measles  as  a  disease  which,  hke 
meningitis,  is  disseminated  throughout  the  civilized  world,  and  which 
although  constantly  with  us  causes  only  sporadic  cases.  True  epi- 
demics of  measles  do  occur,  even  when  there  is  no  gross  change  in  the 
constitution  of  the  population.  We  have  discussed  examples  of  this 
particularly  in  London.  Flare-ups  of  measles  prevalence  are  in  fact 
so  much  the  rule  that  in  certain  locahties  health  officers  anticipate  a 
measles  epidemic  about  once  in  two  years.  Furthermore  measles  has 
been  known  more  than  once  to  occur  in  extensive  epidemic  form, 
attacking  large  proportions  of  the  population  invaded.  We  know  that 
there  is  an  immunity  to  measles  which  is  nearly  absolute  in  those  who 
have  once  acquired  the  disease.  The  epidemics  have,  therefore, 
occurred  exclusively  in  those  locaUties  where  the  proportion  of  immune 
individuals  was  relatively  small.  According  to  Noah  Webster  in  1772 
measles  appeared  in  all  parts  of  America  and  was  accompanied  by  an 
unusuaUy  high  mortahty.  In  Charleston  800  or  900  children  died  of 
the  disease.  The  following  year  measles  "finished  its  course  and  was 
followed  by  a  disorder  of  the  throat." 

In  1781  measles  disappeared  from  the  Faroe  Islands,  and  for  the 
following  sixty-five  years  there  was  not  a  case  of  this  disease  anywhere 
on  any  of  the  seventeen  islands  constituting  the  inhabited  parts  of 
this  group.  When  the  disease  was  finally  re-introduced  into  these 
islands,  it  spread  throughout  the  population,  attacking  practically 
every  individual  in  a  relatively  short  interval  of  time,  showing  a  much 
higher  attack  rate  than  did  influenza  in  1918.  There  was  this  differ- 
ence, that  the  only  individuals  w'ho  did  not  acquire  measles  on  its 
re-introduction  into  the  islands  were  those  who  had  had  it  sixty-five 
vears  before.     Panum  did  not  find  an  authentic  case  of  recurrence 


232  INFLUENZA 

in  the  same  individual.  There  was  not  a  single  instance  of  second 
attack  of  measles,  although  the  shortest  possible  interval  between  the 
previous  attack  and  the  subsequent  exposure  was  sixty-five  years. 

In  1875  measles  first  reached  the  inhabitants  of  the  Fiji  Islands. 
The  disease  was  introduced  by  the  King  of  the  Fiji  Islanders  and  his 
escort,  upon  their  return  from  New  South  Wales.  The  entire  popula- 
tion of  the  islands  was  estimated  at  150,000  and  it  is  officially  stated 
that  there  were  40,000  deaths  from  measles  in  the  ensuing  period.  In 
certain  islands  and  villages  where  more  exact  information  was  secured, 
it  was  found  that  from  twenty-seven  to  twenty-eight  per  cent,  of  the 
people  died.  Panic,  insanitary  conditions  and  ignorance  of  how  to 
care  for  the  sick  resulted  in  this  high  mortality.  V.  C.  Vaughan  has 
remarked  that  when  measles  is  introduced  into  a  population  with  a 
susceptibiHty  of  100  per  cent,  "it  strikes  down  so  many  at  practically 
the  same  time  that  adequate  care  for  the  sick  is  impossible."  The 
rapidity  with  which  the  population  is  invaded  is  practically  as  great  as 
it  is  during  influenza  epidemics. 

It  is  the  opinion  of  the  author  that  the  phenomenon  which  cont- 
ributes chiefly  to  the  occurrence  of  influenza  in  epidemics  and  pandemics, 
and  which  causes  the  characteristic  curves  of  a  primary  influenza  wave, 
is  the  absence  of  any  permanent  immunity^  We  have  shown  in  our 
discussion  that  no  immunity  is  proven  to  exist  after  a  year  and  a  half 
or  two  years  at  the  most.  Measles  occurring  in  a  non-immutie  popula- 
tion spreads  through  that  population  with  the  same  high  rate  as  does 
the  influenza.  In  Charts  XXVIII  and  XXIX  we  find  the  curves  of 
incidence  of  measles  in  certain  of  the  United  States  Army  camps 
in  the  fall  and  winter  of  1917-18.  The  simplest  curve  is  that  for  Camp 
Wheeler.  Here  the  type  is  similar  to  that  found  in  the  primary  wave 
of  influenza.  There  is  a  quasi-symmetrical  evolution  and  the  concen- 
tration is  closely  grouped  around  the  maximum.  The  total  duration 
of  the  epidemic  is  short,  not  being  much  over  eight  weeks.  The  troops 
at  this  camp  were  predominantly  rural.  The  disease  starting  in  this 
group  of  relatively  non-immunes  spread  rapidly  until  presumably  all 
susceptible  material  was  exhausted.  Compare  Camp  Wheeler  with 
those  camps  where  the  population  was  chiefly  urban.  Here  the  wave 
is  of  longer  duration,  is  not  as  high,  the  increase  is  slower,  the  decrease 
is  more  gradual  and  the  concentration  is  not  grouped  so  closely  about 
the  maximum.  In  the  case  of  the  other  camps  with  chiefly  rural 
population,  the  curve  is  not  as  simple  as  is  the  case  with  Camp  Wheeler, 
and  there  are  at  times  secondary  curves  as  in  the  case  of  Camp  Bowie, 
but  the  essential  similarity  to  the  curve  at  Camp  Wheeler  and  the  dif- 


CHART  XXVIII. 


VM 

3100 
JOOQ 

/eoa 
j7ao 

/6CC 

/soo 
/vaa 

/300 
IfOO 

soo 
BOO 
7O0 
600 

500 
400 
3aO 


1  Res(Di  ra-tor^/ D  i^ease    at   Army    Cann|os 


/>JOO 
/906 

/eao 
/sa6 

AtffO 
1300 
I2O0 

//oo 

/0OO 

90a 

MO 

6og 

fOO 

•400 
300 

2oa 
/ao 


Co mp  Bowie  [N.GJ 


Zexc^-s 


Measles  - 
Pneumonia 


I  r       1 

Camp  Wheeler[N.G]  |i    Camp  Travis    [N-AJ 


C.  Beau  rego  rd[N.Gr| 

Z.  o^/.s/O'/ycr 
A^/Jss/ss.  //<V 


'      "         iJ       N       ^       ^  "v        \  y        ^       1^       >§. 


I 


■5^ 


i 


^ 


CHART  XXIX. 


Sffo 
too 


Res|oiratory  Tlisease  qI  /Arnn^   Camp-S 

Measles 


Camp 
Deven^ 


Pn 


eumonia 


Cqm|o 


400 
30ff 

/OO 


Ca  m|o 
Cutter 


Cam  p 
Gran-h 


7}- 00/3^ 


^////70/s, 


I  \ 
1^1    \ 


AN    EPIDEMIOLOGIC    STUDY  233 

ference  from  the  curves  at  Devens,  Dix,  Custer  and  Grant  is  striking. 
It  may  be  that  the  double  waves  are  explained  by  ac(}uisition  of  new 
i)odies  of  troops,  by  the  introduction  of  new  susceptible  material.  On 
this  question  we  have  no  exact  information. 

This  experience  was  equally  true  during  the  Civil  war.  Although 
there  are  no  exact  reports,  it  appears  that  measles  prevailed  in  the 
Confederate  army  and  was  much  more  highly  fatal  than  in  the  Union 
army. 

A  recurrent  influenza  epidemic  usually  takes  the  form  of  a  second- 
ary wave,  particularly  so  if  it  follows  the  primary  wave  within  a  short 
period  of  time.  The  difference  in  the  character  of  the  wave  is  due  to 
the  fact  that  there  is  still  a  comparatively  large  concentration  of 
immune  individuals,  immunized  by  having  had  the  disease  during  the 
primary  spread.  The  secondary  type  of  the  influenza  wave  corre- 
sponds with  the  measles  curves  for  the  urban  camps.  There  are  all 
gradations  in  influenza  from  the  typical  primary  wave  down  to  a  very 
much  flattened  wave  of  relatively  long  duration,  and  even  on  to  the 
stage  of  endemicity,  with  no  discernible  wave.  In  1920  the  recurrent 
epidemic  partook  more  of  the  form  of  a  primary  wave,  because  in  most 
individuals  the  period  of  immunity  had  been  completed  by  January 
and  February,  1920. 

If  we  could,  by  some  means,  induce  an  immunity  which  would  last 
for  long  periods  of  time,  pandemic  influenza  would  disappear  from  the 
earth  and  the  disease  w^ould  be  relegated  to  the  comparatively  minor 
position  now  occupied  by  measles.  The  disease  would  be  constantly 
endemic,  frequently  breaking  out  in  small  epidemics,  but  never  be- 
coming pandemic.  This  is  one  object  that  should  be  held  in  view  by  the 
immunologists  and  bacteriologists.  But  it  is  not  so  simple.  Even 
were  a  successful  vaccine  discovered,  it  is  doubtful  whether  any  con- 
siderable group  of  the  population  could  be  persuaded  to  take  it  as 
often  as  would  be  necessary.  Universal  vaccination  against  small  pox 
has  never  been  carried  out.  The  same  would  be  true  at  the  present 
time  with  regard  to  influenza. 

There  is  another  similarity  between  measles  and  influenza. 
Measles  is  as  infectious  as  is  influenza.  It  is  as  readily  transmitted 
and  the  mode  of  transmission  is  probably  the  same  or  very  similar.  In 
both  diseases  we  are  made  poignantly  aware  of  the  great  contagiousness 
of  the  disease,  and  yet  in  neither  disease  has  there  ever  been  conclusive 
evidence  of  experimental  transmission  from  man  to  man.  Several 
have  reported  attempts  to  transfer  measles,  but  in  each  case  the 
evidence  of  infection  has  been  incomplete.     The  work  of  Hektoen  has 


234  INFLUENZA 

been  quoted  in  particular,  but  Sellards,  after  carefully  reviewing  his 
work,  concludes  that  the  evidence  of  infection  is  insufficient.  More- 
over Hektoen's  patients  were  not  exposed  subsequently  to  measles 
infection  in  the  natural  way. 

SECTION  VIII. 

The  Prevention  and  Control  of  Influenza. 

Dr.  Hamer  has  visualized  the  present  state  of  our  knowledge  of  epi- 
demic influenza  in  a  manner  which  can  scarcely  be  improved  upon. 
We,  therefore,  quote  him  at  length:  "It  seems  to  me  that,  during  the 
last  thirty  years  or  more,  we  have  been  making  fairly  steady  uphill 
progress  along  the  road  which  constitutes  the  boundary  between  the 
county  of  epidemiology  and  the  county  of  bacteriology,  and  that  we 
have  at  length  reached,  at  a  height  considerably  above  sea  level,  the 
foot  of  the  mountain,  on  the  very  top  of  which  lies  hidden  the  secret  of 
an  'epidemic  constitution,'  and  now  we  are  face  to  face  with  a,  parting  of 
ways.  Straight  ahead. is  the  frowning  height,  its  summit  in  cloud. 
On  the  right  hand  stretches  away  a  fine  road  skirting  the  base  of  the 
mountain.  Along  this  road  we  have  recently  seen  Dr.  Brownlee 
whirled  away  in  his  new  car  'periodogram.'  We  are  all  hoping  to  hear 
more  from  him,  but  as  he  is  still  insisting  upon  the  primary,  if  not  the 
exclusive,  importance  of  continuous  variation  in  the  virulence  of  the 
germ,  we  have  to  realize  that  for  the  time  Dr.  Brownlee 's  road  is 
going  down-hill.  On  the  other  hand,  on  the  left,  there  swerves  away, 
through  the  territory  of  the  old  epidemiology,  another  fine  road, 
which  has  been  explored  more  particularly  by  believers  in  'skiey  influ- 
ences.' So  far  as  it  has  been  traced  this  road  is  as  flat  as  flat  can  be, 
but  of  course  there  is  always  the  possibility  that  after  a  while  it  will 
begin  to  rise,  as  it  skirts  round  the  mountain,  and  leads  to  a  good 
vantage  point  from  which  to  start  climbing.  At  the  risk,  however, 
of  ^  being  laughed  at,  I  venture  to  bring  under  notice  the  very  rough 
and  at  first  sight  unpromising  ground  dirctly  in  front  of  us.  Along 
this  can  be  seen  two  obscurely  marked  sheep  tracks  proceeding  at  any 
rate  onwards  and  upwards.  One  diverges  slightly  towards  the  left 
hand  and  it  has  been  followed  at  various  times  by  De  Schweinitz  and 
others,  naturahsts  bent  on  collecting  'ultravisible  viruses;'  the  second 
track,  directed  rather  more  to  the  right,  has  been  explored  by  Reiner, 
Mtiller,  Massini,  Penfold,  and  others,  workers  at  the  problem  of  dis- 
continuous variation  by  'mutation.'  As  a  matter  of  fact  I  have  reason 
to  believe  that  two  travellers,  each  of  whom  follows  one  of  these  tracks, 


AN    EPIDEMIOLOGIC    STUDY  235 

will  keep  in  sight  of  aiul  after  a  wliile  will  find  that  they  are  approach- 
ing one  another,  aiul  will  ultimately  meet  at  a  small  and  retired  upland 
farm ;  then  after  passing  some  dogs  and  following  the  track  until  clear 
of  all  stone  walls,  they  will  come  right  out  in  open  ground  on  the  face 
of  the  mountain  and  can  start  straight  up  the  steep.  But  it  must  here 
be  pointed  out  that  there  remains  to  be  considered  a  fourth  method  of 
approach  to  the  mountain,  the  most  direct  of  all;  but  that  is  by  aero- 
plane and  is  of  course  only  open  to  those  trained  in  metaphysics  and 
statistical  methods.  Investigators  thus  equipped  are  able  to  rise  in 
the  air,  to  survey  with  careful  scrutiny  the  whole  of  the  ground  beneath 
them  and  to  make  the  best  use  of  details  of  information  obtained  by 
scouting  parties  below.  It  is  to  be  hoped  that  at  no  very  distant  date 
a  survey  of  the  top  of  the  mountain  will  thus  become  an  accomplished 
fact.  Meantime,  those  who  cannot  fly  may  find  useful  employment  in 
examining  the  track  beyond  the  farm.  There  is  the  chance  there 
of  picking  up  facts  relating  to  such  questions  as  the  'parasites  associated 
with  a  parasite,'  symbiosis,  and  the  like;  take,  for  example,  a  sugges- 
tion made  fourteen  or  fifteen  years  ago  that  the  influenza  organism 
may  at  one  time  live  in  association  with  Pfeiffer's  bacillus,  at  another 
with  the  Micrococcus  catarrhalis,  and  so  on;  or  the  throat  distemper 
organism  may  be  yoked  now  with  the  diphtheria  bacillus  and  now  with 
the  Streptococcus  conglomeratus.  (Is  that,  I  wonder,  now  to  be 
regard^  as  a  concept  or  as  an  occurrence  or  happening?)" 

At  best  our  knowledge  of  the  cause  and  manner  of  spread  of  influ- 
enza is  fragmentaiy  and  insufficient.  Attempts  to  outline  a  system  of 
control  and  prevention  based  upon  present  concepts  are  met  with 
many  discouragements.  The  next  pandemic  will  not  be  prevented. 
The  disease  wiU  surely  return.  If  the  interval  be  sufficiently  long  it 
may  find  us  quite  as  unprepared  as  we  were  in  1918.  Discouraging  as 
the  outlook  is  there  are  many  bright  points  upon  which  we  must  base 
our  hopes  for  future  results. 

The  difficulties  are  many:  First  the  diagnosis  of  influenza  is  dif- 
ficult either  in  the  individual  case  or  in  the  form  of  a  mild  epidemic. 
Even  in  1918  the  identification  was  often  not  definitely  made  until 
after  wrecks  had  elapsed.  Second,  we  know  little  concerning  the 
mode  of  transmission  of  the  disease.  We  speak  of  ''respiratory  infec- 
tion." We  believe  that  the  transmission  is  by  a  mechanism  similar  to 
that  for  measles,  but  we  have  never  experimentallj'  transmitted  either 
disease.  The  short  incubation  period  places  us  at  a  great  disadvantage. 
Were  the  interval  between  the  occurrence  of  the  first  case  and  the 
development  of  additional  cases  as  long  as  it  is  in  measles,  the  problem 


236  INFLUENZA 

of  isolation  and  quarantine  would  be  simplified.  As  in  measles  the 
disease  is  probably  very  early  infectious,  presumably  before  acute 
symptoms  develop.  The  majority  of  cases  of  influenza  are  ambulatory. 
Many  individuals  do  not  take  to  their  beds,  but  continue  about  their 
work,  spreading  the  disease  wherever  they  go. 

Again,  we  are  ignorant  of  the  period  of  infectiousness.  Dr.  Mere- 
dith Davies  has  made  observations  indicating  that  a  patient  becomes 
non-infectious  within  one  week  after  the  temperature  has  become 
normal.  How  many  influenza  patients  remain  isolated  throughout 
this  period? 

A  carrier  state  probably  exists  and  plays  a  most  significant  part  in 
the  spread. 

Yet  another  drawback  is  the  apparent  wide  susceptibility  to  the  dis- 
ease. Were  individuals  definitely  immunized  by  one  attack  the  pro- 
portion of  susceptibles  would  be  lessened,  their  concentration  in  a 
population  would  be  decreased,  and  the  probability  of  their  being 
exposed  would  be  proportionately  diminished. 

An  additional  difficulty  is  that  after  an  epidemic  has  once  become 
prevalent,  we  must  combat  not  only  the  virus  causing  the  disease  but 
also  the  secondary  invaders. 

Epidemiologic  work  has  shown  that  crowd  gatherings  are  instru- 
mental in  the  spread  of  influenza.  The  density  of  population  has  not 
been  as  definitely  proven  to  be  a  factor.  Crowding,  howev^,  does 
play  a  part.  Close  crowding  in  communities  must  facilitate  the 
spread,  but  pandemics  of  influenza  were  known  before  the  great 
metropoleis  existed.  Hygienic  conditions  play  their  part  in  the 
etiology.  Finally,  in  the  presence  of  every  serious  epidemic  we  must 
also  combat  the  tendency  to  panic  in  the  population. 

Anticipatory  or  preventive  measures. — It  is  erroneous  today  to 
speak  of  measures  for  the  prevention  of  influenza  in  a  community. 
We  cannot  prevent  the  disease.  At  most,  we  can  anticipate  the  occur- 
rence of  an  epidemic  and  take  precautionary  measures  by  which  the 
spread  and  the  severity  of  the  disease  may  be  minimized. 

First  and  foremost  comes  education.  Education  of  the  public,  of 
the  medical  profession  and  of  health  authorities.  "  Scare  headlines  " 
in  the  newspapers  during  epidemics  should  be  discouraged.  Health 
cartoons  are  of  value,  but  when  they  express  only  partial  truths  they 
cannot  but  do  some  harm.  General  education  in  hygienic  methods  and 
in  a  knowledge  of  the  spread  of  contagious  diseases  has  already  been 
most  productive.  Many  methods  by  which  the  public  intelligence 
could  be  reached  are  as  yet  untried.     A  daily  paper  in  Boston  devotes 


AN    EPIDEMIOLOGIC    STUDY  237 

two  columns  a  wook  to  a  discussion  of  public  health  problems,  under 
the  title  of  "The  Clinic."  The  statements  appearing  in  these  columns 
are  nearly  always  the  truth  and  are  not  exaggerations.  There  are 
discussions  of  recent  scientific  work  of  interest  to  the  reading  public. 
As  has  been  emphasized  by  Carnwath,  a  page  devoted  to  methods  of 
maintaining  the  health  of  the  community  would  probably  be  of  more 
immediate  value  than  are  the  many  pages  devoted  to  financial  state- 
ments, "such  as  the  price  of  Mexican  Eagles  or  of  Peruvian  Corpora- 
tion Preference." 

The  organization  of  health  services  to  combat  unexpected  epidemics 
would  be  of  great  assistance.  In  times  of  peace,  prepare  for  war.  In 
all  but  the  largest  cities  the  health  authorities  are  generally  so  free 
from  contact  with  epidemics  and  are  so  pressed  with  routine  that  they 
do  not  organize  in  readiness  for  an  epidemic  which  may  not  come. 
There  should  be  a  closer  co-operative  organization  between  health 
officials  and  practising  physicians,  so  that  the  latter  may  aid  to  a 
greater  extent  in  the  public  health  work.  The  physician  co-operates  in 
furnishing  information  required  by  the  health  officer,  but  too  frequently 
takes  little  interest  in  what  further  is  done  with  this  information.  The 
medical  profession  should  be  made  to  understand  the  importance  of 
public  health  work,  should  have  a  general  comprehension  of  the 
methods  used  in  its  execution  and  should  particularly  develop  a 
sympathetic  and  co-operative  mental  attitude. 

The  medical  societies  of  the  country  should  be  so  organized  that  at 
a  moment's  notice  their  membership  can  be  mobilized  for  the  defense 
of  the  community.  There  is  much  that  the  practising  physician  does 
not  know  about  influenza.  One  of  the  leading  internists  in  one  of  our 
largest  cities,  during  the  1920  epidemic,  refused  to  call  his  cases  influ- 
enza and  treated  them  as  mild  "grip."  It  is  stated  that  he  lost  an 
unusually  large  number  of  his  patients.  There  are  still  many  who 
believe  that  the  two  diseases  are  not  identical.  Not  only  is  this 
detrimental  to  the  patient,  but  as  it  results  in  faliure  to  isolate  the  sick 
it  is,  detrimental  to  the  community. 

Nursing  groups  should  be  organized  to  aid  at  a  moments  notice. 

Much  work  has  been  done  and  great  experience  gained  by  both  the 
physicians  and  the  nursing  organizations  during  the  last  epidemic. 
Now  is  the  time  to  prepare  for  the  next  epidemic  or  pandemic.  With 
the  remembrance  of  1918  fresh  in  our  minds  we  can  establish  a  work- 
ing system,  while  if  we  delay  until  the  expected  arrival  of  another 
epidemic  much  of  our  painfully  acquired  knowledge  will  have  been 
forgotten. 


238  INFLUENZA 

Opinion  differs  as  to  whether  influenza  should  be  made  a  reportable 
disease.  The  added  expense  would  be  not  insignificant.  This  parti- 
cular malady  presents  the  additional  complication  of  being  difficult 
of  diagnosis.  The  records  would  at  best  be  inaccurate.  The  author 
beheves  that  certain  experiments  in  reporting  the  disease  even  in 
inter-epidemic  times  should  be  carried  out.  This  should  be  done  by 
competent  epidemiologists  who  could  later  formulate  plans  for  the 
permanent  reporting  of  the  disease.  We  will  discuss  this  further  under 
the  heading,  "Constructive  Research." 

The  use  of  vaccines  has  been  tried.  In  1918  it  was  almost  uni- 
versally begun  too  late — after  the  epidemic  had  become  prevalent. 
Prophylactic  vaccination  should  be  inaugurated  before  the  disease 
actually  becomes  epidemic.  Vaccination,  particularly  against  the 
secondary  invaders,  is  entirely  rational.  It  may  not  prevent  influ- 
enza, but  it  may  protect  against  the  serious  complications  in  individu- 
als and  may  prevent  to  an  extent  the  spread  of  secondary  invaders  in 
the  community. 

Greenwood  aptly  remarks  that,  "In  estimating  the  total  effects 
produced  upon  morbidity  and  mortality  by  disease,  the  non-specific 
secondary  invaders  are  as  important  as  the  specific  causes.  The  camp 
followers  of  an  army  may  do  more  damage  than  the  regular  soldiers, 
and  the  same  camp  followers  may  ravage  in  the  wake  of  different 
armies." 

At  a  conference  held  at  the  London  War  Office,  October  14,  1918, 
the  subject  of  vaccination  for  influenza  was  discussed.  It  was  decided 
that  only  three  organisms  should  be  employed  in  each  case  in  the 
preparation  of  the  vaccine ;  that  these  races  should  be  recently  isolated 
from  cases  of  the  disease  developing  during  the  course  of  the  epidemic 
and  that  the  microorganisms  should  be  submitted  to  a  rigorous  study 
as  to  race  and  type.  The  first  dose  should  include  30,000,000  of 
Bacillus  influenzae,  100,000,000  pneumococcus,  40,000,000  strepto- 
coccus; the  second  dose  60,000,000  Bacillus  influenzae,  200,000,000 
pneumonococcus,  50,000,000  streptococcus.  The  vaccine  should  be 
sterilized  at  55°  C.  and  one-half  per  cent,  phenol  should  be  added. 
The  administration  should  be  at  ten  days'  intervals. 

In  the  United  States  the  vaccines  employed  have  often  contained  a 
greater  variety  of  organisms.  It  is  unnecessary  to  enumerate  the 
results  obtained  by  various  investigators.  Some  have  been  mildly 
enthusiastic,  while  others  have  obtained  no  demonstrable  benefit. 
It  will  suffice  to  say  that  there  has  been  no  clear  evidence  that  vaccina- 
tion has  been  beneficial,  but  that  the  procedure  has  not  been  giyen  a 


AN    EPIDEMIOLOGIC    STUDY  239 

thorough  trial.  If  the  causative  organism  of  the  disease  is  eventually 
determined,  vaccination  will  probably  be  attempted  with  it  as  antigen. 
For  the  success  of  vaccination  it  is  important  that  practically  entire 
communities  be  inoculated,  and  that  they  be  so  inoculated  before  the 
development  of  epidemic  prevalence. 

Palliative  measures  in  the  -presence  of  an  epidemic. — An  epidemic, 
once  having  obtained  a  start  will  run  its  course.  Our  attempts  will 
be  to  lessen  its  extent  and  diminish  its  explosiveness.  Or,  more  probably, 
we  will  best  succeed  by  extending  the  duration  and  making  the  invasion 
less  explosive.  We  must  know  of  its  earliest  appearance.  Notifica- 
tion must  be  made  by  physicians  to  the  health  authorities  in  order  that 
the  earliest  increase  may  be  detected.  This  again  renders  the  report- 
ing of  the  disease  at  all  times  an  essential  feature.  The  administrative 
control  and  the  puhlicity  to  be  given  have  already  been  discussed. 

What  general  measures  should  be  taken  against  the  disease? 
Should  the  public  schools  be  closed?  Winslow  and  Rogers  found  that 
the  orthodox  methods  of  combating  epidemics  applied  in  Connecticut 
exerted  no  appreciable  influence  on  the  spread  of  influenza.  Bridge- 
port, Hartford  and  New  Haven  did  not  close  their  schools  and  suffered 
from  death  rates  near  the  average  for  the  State,  lower  than  the  rates 
which  prevailed  in  cities  like  Ne^v  London  and  Waterbury,  which 
closed  their  schools.  No  deductions  can  be  drawn  from  this  fact, 
however,  because  the  closing  of  the  schools  in  most  cases  was  forced 
because  of  the  severity  of  the  outbreak. 

The  data  obtained  by  Jordan  indicate  that  schools  were  not 
important  distributing  centers  for  the  infection.  No  explosive  out- 
break occurred  in  any  one  grade,  and  the  four  days  of  the  Thanks- 
giving holiday  evidently  afforded  more  favorable  opportunities  for 
infection  than  did  the  days  of  regular  school  attendance. 

Carnwath  believes  that  in  view  mainly  of  the  marked  prevalence 
of  the  disease  amongst  school  children,  the  balance  of  opinion  is  in 
favor  of  closure,  even  in  densely  populated  urban  districts.  In  the 
author's  investigation  there  was  a  sHghtly  higher  incidence  of  the 
disease  among  children  attending  school  than  among  those  younger 
children  who  were  not  at  school.  The  spread  is  probably  not  facili- 
tated so  much  in  the  class  room  as  it  is  on  the  play  ground.  In  the 
school  room  the  children  are  constrained  to  remain  at  a  certain  distance 
from  each  other.  Probably  they  would  come  into  as  close  contact 
with  cases  if  they  were  not  at  school.  Certainlj'  it  has  not  been 
demonstrated  that  the  school  room  is  a  factor  of  great  importance  in 
the  spread  of  influenza.     It  would,  perhaps,  be  better  not  to  close  the 

19 


240  INFLUENZA 

schools  in  the  presence  of  an  epidemic,  but  to  discontinue  any  congre- 
gation on  the  play  grounds,  and  to  discourage  the  grouping  of  children 
in  play  on  the  streets. 

With  children  and  with  all  individuals,  large  or  small,  a  great 
factor  in  exposure  and  probably  in  the  transmission  of  the  disease  is 
the  necessary  crowding  on  street  cars  and  in  public  buildings.  Here  is  a 
potent  source  which  requires  deep  study  and  new  treatment.  Some 
cities  have  with  partial  success  attempted  lessening  the  congestion 
in  public  conveyances  at  the  beginning  and  closing  of  business  hours 
by  arranging  with  the  various  offices,  stores,  etc.,  that  the  opening  and 
closing  times  occur  at  different  hours.  In  order  that  this  procedure 
may  work  it  is  important  that  the  employees  of  a  factory  or  store  which 
closes  early  must  ride  to  their  destination  at  the  time  of  closing  and 
not  remain  in  the  congested  business  districts.  Here  again  it  is  a 
problem  of  educating  the  public  to  a  point  where  they  will  co-operate 
intelligently. 

It  has  been  amply  demonstrated  that  croivd  gatherings  markedly 
facilitate  the  spread  of  the  disease.  Mass  meetings  should  be  pro- 
hibited and  gatherings  in  and  out  of  doors  should  be  discouraged. 
The  pubhc  should  be  taught  that  the  safest  place  is  at  home. 

What  instructions  can  we  give  to  the  individual  for  his  own  protec- 
tion? There  are  at  least  six  precautions  based  on  scientific  knowledge. 
They  are : 

First:       Avoid  crowds. 

Second:  Avoid  crowding  in  the  family. 

Third:     Sleep  alone. 

Fourth:  Pay  particular  attention  to  personal  hygiene. 

Fifth:      Boil  all  dishes,  etc.,  after  meals. 

Sixth:      Do  not  eat  in  insanitary  restaurants.     Eat  at  home. 

Should  cases  be  isolated?  Should  they  be  quarantined  until  no 
longer  infective?  The  experience  of  the  last  epidemic  has  rendered  us 
pessimistic.  We  have  found  that  isolation  and  quarantine  does  little 
or  no  good.  Institutions  which  were  held  under  rigid  quarantine  for 
the  first  months  of  the  epidemic  were  later  invaded  when  discipline 
became  lax.  The  disease  thereafter  spread  often  as  extensively  as  it 
would  have,  had  there  been  no  delay.  But,  on  the  other  hand,  there 
is  record  of  some  institutions  in  which  the  quarantine  lasted  throughout 
the  epidemic  and  in  which  the  inmates  never  became  ill.  All  of  our 
past  experience  with  infectious  diseases  leads  us  to  believe  that  isola- 
tion of  cases  should  be  enforced.  The  experience  of  1918  should  not 
cause  us  to  change  from  this  point  of  view.     Up  until  now  the  pro- 


AN    EPIDEMIOLOGIC    STUDY  241 

cedure  has  been  without  results.  It  has  been  nearly  impossible  to 
enforce  it.  Further  study  must  be  made  before  any  definite  conclusion 
can  bo  reached. 

Tiio  same  in  general  may  be  said  regarding  disinfection  after  re- 
covery of  a  case  of  influenza.  Today  most  people  believe  that  disin- 
fection is  unnecessary.  The  work  of  Lynch  and  Gumming,  if  correct, 
would  indicate  the  contrary.  The  possibility  of  transmission  through 
inanimate  objects  has  not  as  yet  been  completely  eliminated. 

The  efficacy  of  face  masks  is  still  open  to  question.  Certainly  the 
face  mask  as  extensively  used  during  the  1918  epidemic  was  of  little 
benefit  and  in  many  cases  was,  without  doubt,  a  decided  detriment. 
The  same  mask  was  worn  until  it  was  filthy.  It  was  not  worn  in  such 
a  way  as  to  be  a  protection.  Even  had  the  nose  and  mouth  been 
efficiently  protected,  the  conjunctivae  remained  unprotected.  The 
work  of  Maxcy  and  of  Vincent  and  others  has  demonstrated  the 
importance  of  the  naso-lachrymal  duct  as  a  possible  portal  of  entry 
into  the  respiratory  tract  proper.  After  cultures  of  Bacillus  prodigio- 
sus  were  sprayed  upon  the  ocular  conjunctivae  these  organisms  have 
been  recovered  from  the  nose  within  five  minutes,  from  the  naso- 
pharynx within  fifteen  minutes  and  from  the  feces  within  twenty-four 
hours.  One  difiiculty  in  the  use  of  the  face  mask  is  the  failure  of  co- 
operation on  the  part  of  the  public.  When,  in  pneumonia  and  influ- 
enza wards  it,  has  been  nearly  impossible  to  force  the  orderlies  or  even 
some  of  the  physicians  and  nurses  to  wear  their  masks  as  prescribed, 
it  is  difficult  to  see  how  a  general  measure  of  this  nature  could  be 
enforced  in  the  community  at  large.  If  masks  are  to  be  used  they 
should  be  employed  in  the  same  manner  as  for  protection  against  the 
plague.  They  should  be  made  to  cover  the  entire  head.  This  pro- 
cedure has  been  recommended  particularly  by  Vincent  and  by  Thome. 

It  is  safe  to  say  that  the  face  mask  as  used  was  a  failure. 

Problems  for  the  future.  Constructive  research. — While  pure  epi- 
demiologic study  of  influenza  will  not  demonstrate  the  causative 
agent,  it  is  the  chief  procedure  upon  which  we  can  at  present  rely  for 
improvement  in  our  methods  of  combat.  Many  important  laboratory 
contributions  have  been  made  during  the  last  two  years.  The  ma- 
jority have  been  without  immediate  value  to  the  health  officer.  The 
author  suggests  in  the  following  paragraphs  a  plan  of  study,  based 
upon  past  epidemics  and  the  experiences  of  the  last  pandemic,  as 
epitomized  in  the  preceding  chapters.  During  the  exposition  of  this 
subject  we  have  drawn  certain  conclusions  and  have  developed  some 
theories.     We  beheve  that  they  explain  the  facts  correctly,  but  should 


242  INFLUENZA 

the  hypotheses  prove  not  entirely  correct  the  value  of  the  following 
outHne  for  study  will  be  in  no  way  impaired. 

To  become  thoroughly  acquainted  with  epidemic  influenza  in  all  its 
manifestations  would  require  a  life  time  of  study.  Knowledge  of  the 
disease  would  be  greatly  furthered  if  competent  epidemiologists  should 
see  fit  to  devote  their  entire  time  to  a  study  of  the  disease  in  its  various 
ramifications.  The  author  suggests  a  research  organization  of  indi- 
viduals whose  function  it  would  be  to  become  completely  acquainted 
with  influenza.  The  organization  should  be  under  the  direction  of  a 
competent  board  of  epidemiologists.  Under  them  would  work  several 
groups  composed  of  epidemiologists,  bacteriologists  and  others. 
There  should  be  suflScient  groups  so  that  they  might  be  distributed  to 
diverse  regions  of  the  earth.  They  should  be  equipped  for  travel, 
with  mobile  bacteriologic  laboratories  and  all  the  necessary  equipment 
for  epidemiologic  surveys,  so  that  at  a  moment's  notice  they  could 
proceed  to  wherever  an  epidemic  of  any  disease  simulating  influenza 
is  reported  to  be  prevalent.  The  working  groups  would  be  under  the 
administrative  control  of  the  central  directors  and  would  make  their 
reports  to  them.  All  groups  should  be  so  distributed  geographically 
as  to  have  easy  and  rapid  access  to  any  community  in  which  an  epi- 
demic might  occur.  They  would  keep  themselves  informed  concerning 
the  disease  prevalence  in  all  communities  under  their  jurisdiction. 
This  would  be  done  through  the  co-operation  of  the  civil  health 
authorities  and  through  the  utilization  of  all  other  available  sources  of 
information.  The  central  board  should  be  constantly  in  touch  with 
the  groups,  so  that  the  infectious  disease  prevalence  in  all  parts  of 
the  world  would  be  known  at  all  times. 

Had  such  an  organization  been  in  existence  during  the  last  thirty 
years,  every  one  of  the  so-called  influenza  epidemics  reported  in  one 
place  or  another  would  have  been  investigated.  Detailed  epidemi- 
ologic, statistical,  demographic  and  bacteriologic  reports  would  have 
been  made.  It  matters  Uttle  how  small  or  insignificant  the  outbreak 
appears  to  be.  Even  the  smallest  have  their  characteristic  features 
and  are  worthy  of  study.  If  we  study  epidemic  influenza  but  once 
in  thirty  years,  we  will  never  become  well  acquainted  with  the  disease. 
We  must  see  it  repeatedly  and  frequently.  If  it  does  not  exist  during 
the  intervals  we  must  study  the  diseases  simulating  it.  It  is  surprising 
how  much  of  the  knowledge  acquired  in  1889  was  forgotten  by  1918. 
Even  some  of  the  more  important  features  had  passed  from  memory. 
Thus  we  find  statements  in  1918  that  the  age  morbidity  was  quite 
different  from  that  in  aU  preceding  epidemics.  Research  into  the 
literature  of  the  past  does  not  corroborate  this  impression. 


AN    EPIDEMIOLOGIC    STUDY  243 

If  influenza  is  scattered  throughout  the  earth  in  mild  form,  it 
would  avail  us  but  little  to  send  a  commission  to  Bokhara  to  study  the 
endemic  focus  supposed  by  some  to  exist  in  Turkestan.  Even  though 
the  disease  were  endemic  in  that  country,  one  would  not  expect  to 
discover  epidemics  there.  The  general  immunity  of  the  population 
in  the  endemic  area  is  probably  increased.  Nevertheless  one  unit 
might  well  be  stationed  in  Turkestan,  there  to  study  the  existing 
conditions  regarding  infectious  diseases. 

There  would  be  ample  work  for  all  groups  at  all  times.  The  study 
would  not  be  limited  to  a  consideration  of  infectious  diseases.  Soci- 
ologic  conditions  may  be  of  importance.  We  have  recorded  instances 
of  this.  Wherever  there  is  an  unusual  concentration  of  large  masses 
of  individuals  the  investigators  should  study  the  results  of  such 
concentration. 

An  advantage  of  this  organization  would  be  that  the  groups  through 
their  central  bureau  would  establish  an  information  bureau  of  infec- 
tious disease  prevalence  analogous  to  the  popular  weather  bureau  of 
today.  They  would  report  the  presence  of  a  cloud  before  it  had 
appeared  on  the  local  horizon. 

In  the  absence  of  any  epidemics  resembling  influenza,  there  would 
be  abundant  opportunity  for  correlated  work.  We  have  mentioned 
the  epidemiologic  resemblances  between  influenza  and  certain  other 
infectious  diseases.  Comparative  study  of  any  or  all  of  them  is  of 
importance.  The  bacteriologist  and  the  immunologist  would  find 
plenty  of  material  in  the  study  of  measles  prevalences.  The  two 
diseases  are  so  similar  in  their  manner  of  spread,  in  the  probable  mode 
of  transmission,  in  their  clinical  characteristics  and  in  the  results  of 
laboratory  attempts  at  transmission,  that  one  must  assume  that  the 
causative  viruses  are  not  dissimilar.  Any  new  facts  that  we  may  gain 
concerning  measles  will  be  of  value  in  the  study  of  influenza. 

IMany  years  could  be  well  devoted  merely  to  a  study  of  immunity 
in  influenza. 

The  results  obtained  by  this  proposed  organization  for  the  investi- 
gation of  influenza  would  be  slow^  in  achievement.  The  study  is  not 
of  a  type  calculated  to  appeal  to  the  popular  imagination.  Com- 
munities in  which  the  dread  of  an  iminent  pestilence  is  not  present 
would  subscribe  with  some  hesitation  to  appeals  for  pecuniary  assist- 
ance. Fortunately,  however,  there  are  in  existence  several  organiza- 
tions already  well  developed  along  these  lines,  organizations  chiefly 
interested  in  certain  other  diseases.  There  can  be  no  doubt  but  that 
at  the  present  time  the  financing  of  such  a  broad  project  could  be 


244  INFLUENZA 

arranged,  and  that  the  groups  could  be  efficiently  organized  on  the 
basis  of  experience  already  gained  in  similar  projects. 

Crookshank  well  remarks  that  our  present  epidemiologic  intelli- 
gence service  is  hardly  superior  to  that  of  a  Meteorologic  Office  which 
only  gives  warning  of  rain  when  unfurled  umbrellas  pass  along  the 
street.  Influenza  will  surely  return.  There  will  be  mild  epidemics 
within  the  next  few  years.  In  time  another  pandemic  will  arrive,  and 
after  it  will  come  pandemic  after  pandemic.  In  1918  as  in  1889  we 
were  caught  unprepared.  Let  us  do  our  utmost  to  prevent  the 
recurrence  of  this  tragedy.  To  delay  is  to  loose  the  valuable  informa- 
tion gained  during  the  last  two  years.  The  future  is  not  without  well 
grounded  hope,  but  success  will  not  be  achieved  until  we  have  attained 
a  much  deeper  understanding  of  the  epidemiology  of  influenza. 


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252  .  INFLUENZA 

Newsholme,  a. 

1920.     Influenza.     A  discussion.     Longmans,  Green  &  Co.,  CII,  80. 

1907.     Influenza  from  a  public  health  standpoint.     Practitioner,  118. 

1919.     Jour.  Am.  Med.  Ass.,  LXXIII,  890. 

1919.     Influenza  from  a  public  health  standpoint.     Practitioner,  CII,  6. 
Niemann  and  Foth. 

1919.     Deutsche  Med.  Woch.,  XLV,  471. 
Office  International  d'HygiJine  Publique. 

1918.  X,  also  Jan.  and  Feb.,  1920,  XII. 
Opie,  Freeman,  Blake,  Small  and  Rivers. 

1919.  Pneumonia  at  Camp  Funston.     Report  to  Surgeon  General.     Jour. 

Am.  Med.  Ass.,  LXXII,  108. 
1919.     Pneumonia  following  influenza  at  Camp  Pike,  Ark.     Ibid.,  556. 
Orticoni,  a.,  Barbie  and  Ang6. 

1919.     Pathogenesis  of  influenza.     Abst.  in  Jour.  Am.  Med.  Ass.,  LXXIII, 
69. 

OVAZZA,    V.    E. 

1919.     Prophylaxis  of  influenza.     Abst.  in  Jour.  Am.   Med.  Ass.,  LXXII, 
1335. 
Parkes,  Edmund  A. 

1876.     "Influenza"  in  Reynolds'  System  of  Medicine.     I,  28. 
Parsons,  H.  Franklin. 

1893.     Local    Government    Board    Reports.     C-6387    (1891)    and    C-7051 

(1893). 
1893.     A  further  report  on  the  influenza  epidemics  of  1889-90,   1891  and 
1891-92.     Local  Government  edition.     London,  1893. 
Parsons,  H.  C. 

1919.     Official  report  on  the  influenza  epidemic  1918.     Canad.  Med.     Ass. 
Jour.,  Toronto,  IX,  351. 
Pearl,  Raymond. 

1919.  On  certain  general  statistical  aspects  in  the  1918  epidemic  in  American 

cities.     Public  Health  Reports,  Aug.  8,  1919. 
Peck,  J.  H. 

1920.  Relation  of  influenza  to  tuberculosis.     Iowa  State  Med.  Soc.  Jour., 

X,  42. 
Pehu,  M.  and  Ledoux,  E. 

1918.     Revue  documentaire  sur  I'epidemie  actuelle  de  grippe  en   France. 

Ann.  de  Med.,  V,  579. 
Pneumonic  Plague. 

1918.  China  Med.  Jour.,  XXXII,  146. 
Pollard,  R. 

1920.     Control  of  influenza.     Brit.  Med.  Jour.,  I,  258. 
Pruvost,  E. 

1919.  Considerations  inspirees  par  la  recente  epidemie  de  grippe  sur  la 

pathogenie  de  cette  maladie  et  sur  celle  de  la  tuberculose.     Bull. 
et  Mem.  Soc.  Med.  des  Hop.  de  Paris,  3  s.,  XLIII,  783. 
Raffelt,  F. 

1920.  Influenza  Epidemie,  1918.     Wien.  klin.  Woch.,  XXXIII,  April  15. 


lUHIilOCHAI'llY  253 

R6non,  L.  and  Mm  not,  1{. 

1920.     La  grippe  de  1920  a  riiopital  Xcckor.     Bull,  et  Mem.  Soc.  Med.  dcs 
H6p.  de  Paris,  509. 
Prevention  Bukeau. 

1918.  Report  of  the  Shansi  Plague.     China  Med.  Jour.,  XXXII,  559. 

RotTSSY,    B. 

1919.  Nature  et  modes  d'action  de  I'agent  pathog^ne  infectieux  de  la  grippe 

ou  influenza.     Rev.  d'hyg.,  XLI,  104. 
Rose,  F.  G. 

1919.     The  influenza  epidemic  in  British  Guiana.     Lancet,  I,  421. 
ROSENATJ,    M.   J. 

1919.     Experiments  to  determine  the  mode  of  spread  of  influenza.     Jour. 
Am.  Med.  Ass.,  LXXIII,  311. 
ROSENOW,   E.    C. 

1919.     Prophylactic  inoculation  against  respiratory  infections.     Jour.  Am. 
Med.  Ass.,  LXXII,  31. 
Roys,  Chas.  K. 

1918.  Report  on  epidemic  of  pneumonic  plague  in  Tsinauflu,  1918.     China 

Med.  Jour.,  XXXII,  346. 

RUHRAH,    J. 

1919.  Some  of  the  aspects  of  epidemic  influenza  in  children.     Med.  Clin. 

North  Am.,  II,  1597. 
Rtjssell,  W. 

1919.     Some  aspects  of  the  influenza  epidemic.     Lancet,  I,  690. 
Robertson,  Jno.  D.,  and  Koehler,  Gottfried. 

1918.  Preliminary  report  on  the  influenza  epidemic  in  Chicago.     Am.  Jour. 

Pub.  Health,  VIII,  849. 

RONDOPOULOS,    P.    J. 

1919.  Influenza  in  Greece.     Abstr.  in  Jour.  Am.  Med.  Ass.,  LXXII,  1947. 
Sahli,  H. 

1919.     Influenza.     Abstr.  in  Jour.  Am.  Med.  Ass.,     Ibid.,  687. 
Sanz,  E.  F. 

1919.     Jacksonian  epilepsy  following  influenza.     Abstr.  in  Jour.  Am.    Med. 
Ass.,  LXXIII,  73. 

SCHOFIELD,    F.    W.    AND    CyNN,    H.    C. 

1919.     Pandemic  influenza  in  Korea.     Jour.  Am.  Med.  Ass.,  LXXII,  981. 
ScocciA,  V. 

1919.     Does   influenza    confer  immunity?     Abstr.  in  Jour.  Am.   Med.  Ass. 
Ibid.,  529. 
Selter,  H. 

1918.  Zur  Aetiologie  der  Influenza.     Deutsch.  Med.  Woch,  XLIV,  932. 
Sherman,  C.  L. 

1913.     Common  infections  that  are  often  erroneously  diagnosed   as  grip. 
Jour.  Am.  Med.  Ass.,  LXI,  1567. 
Siciliano,  L. 

1919.  Qualche    osservazione    suU'epidemiologia    dell'influenza.     Riv.    crit. 

di  Clin.  Med.  Firenze,  XX,  97. 
Silvestri,  I. 

1919.     Quinine,    malaria   and   influenza.     Abst.    in   Jour.    Am.    Med.    Ass., 
LXXIII,  304. 


)■ 
254  INFLUENZA  ! 

I 

Small,  W.  D.  D. 

1920.     Clinical  features,  etiology  and  treatment  of  influenza.     Edinb.  Med. 
Jour.,  XXV,  15. 
Smith,  Theobold. 

1904.  Some  problems  in  the  life  history  of  pathogenic    microorganisms. 

Am.  Med.,  711. 

SOLDAN,    C.    E. 

1919.     Influenza  in  Lima.     Abstr.  in  Jour.  Am.  Med.  Ass.,  LXXII,  970. 
SoPER,  George  A. 

1919.     The  influenza  pneumonia  pandemic  in  the  American  Army  camps 

during  September  and  October,   1918.     Science,  N.  S.,  XLVIII, 

451. 
1919.     The  efficiency  of  existing  measures  for  the  prevention  of  disease. 

Jour.  Am.  Med.  Ass.,  LXXIII,  1405. 
1919.     What  is  influenza?     Boston  Med.  and  Surg.  Jour.,  CLXXXI,  635. 

1919.  Influenza  in  horses  and  in  man.     N.  Y.  Med.  Jour.,  CIX,  270. 
Speak,  B.  E. 

1920.  The  periodicity  of  influenza.     Lancet,  I,  889. 
Spooner,  L.  H.,  Scott,  J.  M.  and  Heath,  E.  H. 

1919.  A  bacteriologic  study  of  the  influenza  epidemic  at  Camp  Devens, 

Mass.     Jour.  Am.  Med.  Ass.,  LXXII,  155. 
Stallybrass,  C.  O. 

1920.  The  periodicity  of  influenza.     Lancet,  CXCVIII,  372. 
Stanley,  Arthur. 

1918.  Notes  on  pneumonic  plague  in  China.     China  Med.  Jour.,  XXXII, 

207. 
Stanley,  L.  L. 

1919.  Influenza  at  San  Quentin  Prison,  California.     Public  Health  Reports, 

XXXIV,  996. 
Stivelman,  B. 

1919.  Effects  of  influenza  on  pulmonary  tuberculosis.     New  York  Med. 

Jour.,  LX,  20. 
Sturrock: 

1905.  Notes  on  an  epidemic  of  influenza,  occurring  in  the  Midlothian  and 

Peebles  Asylums.    Brit.  Med.  Jour. 
Sydenstricker,  Edgar. 

1920.  Difficulties  in  computing  civil  death  rates  for  1918  with  especial 

reference  to  epidemic  influenza.     Public  Health  Reports,  XXXV, 
330. 

1918.  Preliminary    statistics    of   the    influenza   epidemic.     Public    Health 

Reports,  XXXIII,  2305. 
Teissier,  J. 

1920.     La  grippe  paraUele  des  deux  grandes  pand^mies  de  1889  et  de  1918. 
Paris  M6d.,  XXXV,  69. 
Telling,  W.  H.  M.  and  Hann,  R.  G. 

1913.     Influenza  with  repeated  rigors.     Practitioner,  764. 
de  LOS  Tbrreros,  C.  S. 

1919.  Influenza  in  children.     Abstr.  in  Jour.  Am.  Med  Ass.,  LXXII,  764 
TOPLEY,   W.    W.   C. 

1919.     The  spread  of  bacterial  infection.    Lancet,  II,  1,  45,  91. 


BIBLIOtJHAIMlY  2^)^^ 

UsiTKUT,     V. 

1U19.  InfiiKMizii  ill  Norway.      Al)str.  in  Juur.  Am.  .Med.  A>.s.,  I. XXII,  111.'.. 

Vauoh.\n,  Henhy  F. 

1920.  Influenza  in  Detroit.     Weekly  health  reports,  Commissioner  of  Health, 
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Vaughan,  V.  C. 

1918.  An  explosive  epidemic  of  influenzal  disease  at  Fort  Oglcthf»rpp.     Jour. 
Lab.  and  Clin.  Med.,  Ill,  560. 

1918.  The  influenza  in  Germany,     Ibid.,  IV,  83. 

1918.  Notes  on  influenza.     Ibid.,  145. 

1918.  Influenza  and  pneumonia  at  Bre.st,  France.     Il)id.,  223. 

1918.  Influenza  at  Camp  Custer.     Ibid.,  225. 

1918.  Influenza  and  pneumonia  at  Camp  Grant.     Ibid.,  306. 

1918.  Notes  on  influenza.     Ibid.,  309. 

1918.  Encephalitis  lethargica.     Ibid.,  381. 

1919.  Jour.  Am.  Med.  Ass.,  LXXIII,  890. 
Vaughan,  V.  C.  and  Palmer,  Geo.  T. 

1919.     Communicable  diseases  in  the  United  States  Army  during  the  summer 
and  autumn  of  1918.     Joiir.  Lab.  and  Clin.  Med.,  IV,  .586. 

1918.  Communicable  diseases  in  the  National  Guard  and  National  Army 

of  the  United  States  during  the  six  months  from  Sept.  29,  1917,  to 
March  29,  1918.     Jour.  Lab.  and  Clin.  Med.,  Ill,  635. 
Vaughan,  W.  T.  and  Schnabel,  T.  G. 

1919.  Pneumonia  and  empj-ema  at  Camp  Sevier.     Arch.  Int.  Med.,  XXII, 

44L 
Vaughan,  W.  T. 

1918.  Chnical  manifestations  of  empyema.     Jour.  Lab.   and  Clin.   Med., 

IV,  123. 
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1919.  Quinine    and    influenza.    Abstr.    in   Jour.    Am.    Med.   Ass.,  LXXII, 

1648. 
Wadsworth,  a,  B. 

1919.     Results  of  preventive  vaccination  with  suspensions  of  the  influenza 
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Wahl,  H.  R.,  White,  B.  and  Lyall,  H.  W. 

1919.     Some  experiments  in  the  transmission  of  influenza.     Jour.  Inf.  Di.s., 
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Walb. 

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Wallace,  Geo.  L. 

1919     Report  of  the  influenza  epidemic  and  experience  in  the  u.se  of  influenza 
vaccine  "B"  at  the  Wrentham  State  School.     Boston  Med.  and 
Surg.  Jour.,  CLXXX,  447. 
W^atson,  Thomas. 

1872.     Principles  and  Practice  of  Physic.     II,  71. 
Watson,  Percy  T. 

1919.     The  epidemic  in  Shansi;  pneumonic  plague  or  influenza?     China  Med. 
Jour.,  XXXIII,  169. 

20 


256  INFLUENZA 

Webster,  J.  O. 

1871.     Report  of  an  epidemic  of  influenza.     Boston  Med.  and  Surg.  Jour., 
N.  S.,  VII,  377. 
WiNSLow,  C.  E.  A.  AND  Rogers,  J.  F. 

1920.     Statistics  of  the  1918  epidemic  of  influenza  in  Connecticut.     Jour. 
Infect.  Dis.,  XXVI. 

WOLLSTEIN,    M.    AND    GoLDBLOOM,    A. 

1919.     Epidemic  influenza  in  infants.     Am.  Jour.  Dis.  of  Children,  XVII, 
165. 
Woodward,  Wm.  C. 

1918.     Influenza  in  Boston.     Monthly  Bull,  of  the  Health  Dept.  of  the  City 
of  Boston,  VII,  179-186,  205-208,  and  VIII,  10. 
WooLEY,  Paul  G. 

1918.  The  epidemic  of  influenza  at  Camp  Devens,  Mass.     Jour.  Lab.  and 

Clin.  Med.,  IV,  330. 

1919.  An  epidemiologic  fragment.     Med.  Quart.,  Ottawa,  I,  325. 
Zinsser,  H.,  Brooks,  H.,  et  al. 

1920.  Manifestations  of  influenza  during  the  earlier  periods  of  its  appearance 

in  France.     Med.  Rec,  XCVII,  459. 
Zinsser,  Hans. 

Influenza.     Oxford  Medical  Papers  (to  be  pubHshed). 

A  most  comprehensive  bibliography  of  the  literature  covering  the  epidemiology 
of  influenza  up  until  1896  is  to  be  found  in  Leichtenstern's  original  monograph. 


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